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 $7.32   10.773%   $8.1086   $8.11   $8.10   $8.10  
  Purchase #2 $8.59   11.374%   $9.567   $9.57   $9.55   $9.60  
  Purchase #3 $197.98   11.575%   $220.8962   $220.90   $220.90   $220.90  
  Purchase #4 $110.62   9.556%   $121.1908   $121.19   $121.20   $121.20  
  Purchase #5 $190.57   10.401%   $210.3912   $210.39   $210.40   $210.40  
  Purchase #6 $124.61   3.312%   $128.7371   $128.74   $128.75   $128.70  
  Purchase #7 $243.30   13.183%   $275.3742   $275.37   $275.35   $275.40  
  7 purchase totals = $882.99       $974.2651   $974.27   $974.25   $974.30