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 $85.45   10.105%   $94.0847   $94.08   $94.10   $94.10  
  Purchase #2 $132.39   8.717%   $143.9304   $143.93   $143.95   $143.90  
  Purchase #3 $165.68   8.120%   $179.1332   $179.13   $179.15   $179.10  
  Purchase #4 $59.86   5.644%   $63.2385   $63.24   $63.25   $63.20  
  Purchase #5 $235.35   12.375%   $264.4746   $264.47   $264.45   $264.50  
  Purchase #6 $222.87   6.697%   $237.7956   $237.80   $237.80   $237.80  
  Purchase #7 $29.58   10.697%   $32.7442   $32.74   $32.75   $32.70  
  7 purchase totals = $931.18       $1,015.4012   $1,015.39   $1,015.45   $1,015.30