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 $57.55   7.831%   $62.0567   $62.06   $62.05   $62.10  
  Purchase #2 $139.81   10.614%   $154.6494   $154.65   $154.65   $154.60  
  Purchase #3 $82.46   11.444%   $91.8967   $91.90   $91.90   $91.90  
  Purchase #4 $123.60   7.594%   $132.9862   $132.99   $133.00   $133.00  
  Purchase #5 $98.85   5.873%   $104.6555   $104.66   $104.65   $104.70  
  Purchase #6 $115.76   4.704%   $121.2054   $121.21   $121.20   $121.20  
  Purchase #7 $151.33   4.419%   $158.0173   $158.02   $158.00   $158.00  
  7 purchase totals = $769.36       $825.4672   $825.49   $825.45   $825.50