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 $108.94   11.584%   $121.5596   $121.56   $121.55   $121.60  
  Purchase #2 $10.70   11.491%   $11.9295   $11.93   $11.95   $11.90  
  Purchase #3 $219.64   9.705%   $240.9561   $240.96   $240.95   $241.00  
  Purchase #4 $154.94   7.732%   $166.92   $166.92   $166.90   $166.90  
  Purchase #5 $135.31   6.230%   $143.7398   $143.74   $143.75   $143.70  
  Purchase #6 $106.74   5.189%   $112.2787   $112.28   $112.30   $112.30  
  Purchase #7 $214.44   6.568%   $228.5244   $228.52   $228.50   $228.50  
  7 purchase totals = $950.71       $1,025.9081   $1,025.91   $1,025.90   $1,025.90