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 $187.68   7.653%   $202.0432   $202.04   $202.05   $202.00  
  Purchase #2 $120.78   9.266%   $131.9715   $131.97   $131.95   $132.00  
  Purchase #3 $103.53   5.155%   $108.867   $108.87   $108.85   $108.90  
  Purchase #4 $152.88   8.793%   $166.3227   $166.32   $166.30   $166.30  
  Purchase #5 $236.47   3.705%   $245.2312   $245.23   $245.25   $245.20  
  Purchase #6 $246.96   6.821%   $263.8051   $263.81   $263.80   $263.80  
  Purchase #7 $243.52   7.196%   $261.0437   $261.04   $261.05   $261.00  
  7 purchase totals = $1,291.82       $1,379.2844   $1,379.28   $1,379.25   $1,379.20