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 $222.77   10.347%   $245.82   $245.82   $245.80   $245.80  
  Purchase #2 $31.79   4.507%   $33.2228   $33.22   $33.20   $33.20  
  Purchase #3 $175.52   10.576%   $194.083   $194.08   $194.10   $194.10  
  Purchase #4 $154.76   6.811%   $165.3007   $165.30   $165.30   $165.30  
  Purchase #5 $158.82   11.873%   $177.6767   $177.68   $177.70   $177.70  
  Purchase #6 $195.74   4.532%   $204.6109   $204.61   $204.60   $204.60  
  Purchase #7 $120.61   13.572%   $136.9792   $136.98   $137.00   $137.00  
  7 purchase totals = $1,060.01       $1,157.6933   $1,157.69   $1,157.70   $1,157.70