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 $41.26   5.610%   $43.5747   $43.57   $43.55   $43.60  
  Purchase #2 $69.96   12.839%   $78.9422   $78.94   $78.95   $78.90  
  Purchase #3 $68.73   8.205%   $74.3693   $74.37   $74.35   $74.40  
  Purchase #4 $91.47   12.600%   $102.9952   $103.00   $103.00   $103.00  
  Purchase #5 $206.62   10.278%   $227.8564   $227.86   $227.85   $227.90  
  Purchase #6 $142.80   9.729%   $156.693   $156.69   $156.70   $156.70  
  Purchase #7 $78.86   7.265%   $84.5892   $84.59   $84.60   $84.60  
  7 purchase totals = $699.70       $769.0200   $769.02   $769.00   $769.10