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 $154.71   13.802%   $176.0631   $176.06   $176.05   $176.10  
  Purchase #2 $25.72   4.822%   $26.9602   $26.96   $26.95   $27.00  
  Purchase #3 $62.71   6.134%   $66.5566   $66.56   $66.55   $66.60  
  Purchase #4 $146.72   11.421%   $163.4769   $163.48   $163.50   $163.50  
  Purchase #5 $79.85   12.356%   $89.7163   $89.72   $89.70   $89.70  
  Purchase #6 $144.84   11.657%   $161.724   $161.72   $161.70   $161.70  
  Purchase #7 $93.78   9.627%   $102.8082   $102.81   $102.80   $102.80  
  7 purchase totals = $708.33       $787.3053   $787.31   $787.25   $787.40