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 $35.47   13.703%   $40.3305   $40.33   $40.35   $40.30  
  Purchase #2 $138.68   7.587%   $149.2017   $149.20   $149.20   $149.20  
  Purchase #3 $10.52   11.278%   $11.7064   $11.71   $11.70   $11.70  
  Purchase #4 $241.27   12.457%   $271.325   $271.33   $271.35   $271.30  
  Purchase #5 $201.39   5.440%   $212.3456   $212.35   $212.35   $212.30  
  Purchase #6 $237.46   9.837%   $260.8189   $260.82   $260.80   $260.80  
  Purchase #7 $179.60   8.708%   $195.2396   $195.24   $195.25   $195.20  
  7 purchase totals = $1,044.39       $1,140.9677   $1,140.98   $1,141.00   $1,140.80