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 $182.86   8.561%   $198.5146   $198.51   $198.50   $198.50  
  Purchase #2 $222.45   7.333%   $238.7623   $238.76   $238.75   $238.80  
  Purchase #3 $150.97   8.405%   $163.659   $163.66   $163.65   $163.70  
  Purchase #4 $242.87   10.792%   $269.0805   $269.08   $269.10   $269.10  
  Purchase #5 $132.82   9.411%   $145.3197   $145.32   $145.30   $145.30  
  Purchase #6 $68.49   10.441%   $75.641   $75.64   $75.65   $75.60  
  Purchase #7 $60.35   10.432%   $66.6457   $66.65   $66.65   $66.60  
  7 purchase totals = $1,060.81       $1,157.6228   $1,157.62   $1,157.60   $1,157.60