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 $40.93   6.207%   $43.4705   $43.47   $43.45   $43.50  
  Purchase #2 $244.40   13.340%   $277.003   $277.00   $277.00   $277.00  
  Purchase #3 $61.28   11.189%   $68.1366   $68.14   $68.15   $68.10  
  Purchase #4 $102.82   10.847%   $113.9729   $113.97   $113.95   $114.00  
  Purchase #5 $222.59   4.309%   $232.1814   $232.18   $232.20   $232.20  
  Purchase #6 $19.49   4.197%   $20.308   $20.31   $20.30   $20.30  
  Purchase #7 $190.26   13.421%   $215.7948   $215.79   $215.80   $215.80  
  7 purchase totals = $881.77       $970.8672   $970.86   $970.85   $970.90