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 $97.68   5.306%   $102.8629   $102.86   $102.85   $102.90  
  Purchase #2 $161.68   9.270%   $176.6677   $176.67   $176.65   $176.70  
  Purchase #3 $163.50   4.555%   $170.9474   $170.95   $170.95   $170.90  
  Purchase #4 $139.30   4.485%   $145.5476   $145.55   $145.55   $145.50  
  Purchase #5 $244.39   7.603%   $262.971   $262.97   $262.95   $263.00  
  Purchase #6 $52.52   7.797%   $56.615   $56.62   $56.60   $56.60  
  Purchase #7 $133.48   10.688%   $147.7463   $147.75   $147.75   $147.70  
  7 purchase totals = $992.55       $1,063.3579   $1,063.37   $1,063.30   $1,063.30