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 $201.52   11.578%   $224.852   $224.85   $224.85   $224.90  
  Purchase #2 $239.77   6.711%   $255.861   $255.86   $255.85   $255.90  
  Purchase #3 $120.29   4.211%   $125.3554   $125.36   $125.35   $125.40  
  Purchase #4 $55.97   10.564%   $61.8827   $61.88   $61.90   $61.90  
  Purchase #5 $188.72   6.513%   $201.0113   $201.01   $201.00   $201.00  
  Purchase #6 $245.37   9.494%   $268.6654   $268.67   $268.65   $268.70  
  Purchase #7 $185.98   6.534%   $198.1319   $198.13   $198.15   $198.10  
  7 purchase totals = $1,237.62       $1,335.7597   $1,335.76   $1,335.75   $1,335.90