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 $177.56   6.408%   $188.938   $188.94   $188.95   $188.90  
  Purchase #2 $12.50   8.751%   $13.5939   $13.59   $13.60   $13.60  
  Purchase #3 $140.32   7.258%   $150.5044   $150.50   $150.50   $150.50  
  Purchase #4 $72.50   7.555%   $77.9774   $77.98   $78.00   $78.00  
  Purchase #5 $80.28   5.716%   $84.8688   $84.87   $84.85   $84.90  
  Purchase #6 $11.39   12.527%   $12.8168   $12.82   $12.80   $12.80  
  Purchase #7 $94.26   8.261%   $102.0468   $102.05   $102.05   $102.00  
  7 purchase totals = $588.81       $630.7461   $630.75   $630.75   $630.70