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 $219.70   6.801%   $234.6418   $234.64   $234.65   $234.60  
  Purchase #2 $46.96   4.424%   $49.0375   $49.04   $49.05   $49.00  
  Purchase #3 $154.92   7.358%   $166.319   $166.32   $166.30   $166.30  
  Purchase #4 $71.54   7.663%   $77.0221   $77.02   $77.00   $77.00  
  Purchase #5 $45.61   11.417%   $50.8173   $50.82   $50.80   $50.80  
  Purchase #6 $244.43   3.566%   $253.1464   $253.15   $253.15   $253.10  
  Purchase #7 $216.61   11.761%   $242.0855   $242.09   $242.10   $242.10  
  7 purchase totals = $999.77       $1,073.0696   $1,073.08   $1,073.05   $1,072.90