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 $59.93   13.653%   $68.1122   $68.11   $68.10   $68.10  
  Purchase #2 $224.88   5.590%   $237.4508   $237.45   $237.45   $237.50  
  Purchase #3 $232.76   5.702%   $246.032   $246.03   $246.05   $246.00  
  Purchase #4 $177.60   7.557%   $191.0212   $191.02   $191.00   $191.00  
  Purchase #5 $221.57   11.236%   $246.4656   $246.47   $246.45   $246.50  
  Purchase #6 $156.88   13.817%   $178.5561   $178.56   $178.55   $178.60  
  Purchase #7 $59.76   9.408%   $65.3822   $65.38   $65.40   $65.40  
  7 purchase totals = $1,133.38       $1,233.0201   $1,233.02   $1,233.00   $1,233.10