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 $119.52   10.191%   $131.7003   $131.70   $131.70   $131.70  
  Purchase #2 $199.96   4.808%   $209.5741   $209.57   $209.55   $209.60  
  Purchase #3 $78.70   7.808%   $84.8449   $84.84   $84.85   $84.80  
  Purchase #4 $115.79   7.257%   $124.1929   $124.19   $124.20   $124.20  
  Purchase #5 $44.75   7.332%   $48.0311   $48.03   $48.05   $48.00  
  Purchase #6 $62.68   3.649%   $64.9672   $64.97   $64.95   $65.00  
  Purchase #7 $28.52   4.141%   $29.701   $29.70   $29.70   $29.70  
  7 purchase totals = $649.92       $693.0115   $693.00   $693.00   $693.00