Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $232.62   12.312%   $261.2602   $261.26   $261.25   $261.30  
  Purchase #2 $173.48   3.413%   $179.4009   $179.40   $179.40   $179.40  
  Purchase #3 $244.98   9.731%   $268.819   $268.82   $268.80   $268.80  
  Purchase #4 $209.74   6.621%   $223.6269   $223.63   $223.65   $223.60  
  Purchase #5 $150.69   4.801%   $157.9246   $157.92   $157.90   $157.90  
  Purchase #6 $187.52   12.313%   $210.6093   $210.61   $210.60   $210.60  
  Purchase #7 $127.68   13.779%   $145.273   $145.27   $145.25   $145.30  
  7 purchase totals = $1,326.71       $1,446.9139   $1,446.91   $1,446.85   $1,446.90