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 $57.87   5.548%   $61.0806   $61.08   $61.10   $61.10  
  Purchase #2 $201.43   5.721%   $212.9538   $212.95   $212.95   $213.00  
  Purchase #3 $83.50   13.592%   $94.8493   $94.85   $94.85   $94.80  
  Purchase #4 $235.71   11.838%   $263.6133   $263.61   $263.60   $263.60  
  Purchase #5 $60.85   5.348%   $64.1043   $64.10   $64.10   $64.10  
  Purchase #6 $7.78   9.491%   $8.5184   $8.52   $8.50   $8.50  
  Purchase #7 $92.50   4.426%   $96.5941   $96.59   $96.60   $96.60  
  7 purchase totals = $739.64       $801.7138   $801.70   $801.70   $801.70