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 $64.72   10.322%   $71.4004   $71.40   $71.40   $71.40  
  Purchase #2 $194.89   12.709%   $219.6586   $219.66   $219.65   $219.70  
  Purchase #3 $72.53   4.594%   $75.862   $75.86   $75.85   $75.90  
  Purchase #4 $138.32   12.486%   $155.5906   $155.59   $155.60   $155.60  
  Purchase #5 $200.46   9.642%   $219.7884   $219.79   $219.80   $219.80  
  Purchase #6 $113.27   13.416%   $128.4663   $128.47   $128.45   $128.50  
  Purchase #7 $10.44   7.262%   $11.1982   $11.20   $11.20   $11.20  
  7 purchase totals = $794.63       $881.9645   $881.97   $881.95   $882.10