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 $198.46   4.154%   $206.704   $206.70   $206.70   $206.70  
  Purchase #2 $209.88   13.603%   $238.43   $238.43   $238.45   $238.40  
  Purchase #3 $145.38   9.742%   $159.5429   $159.54   $159.55   $159.50  
  Purchase #4 $120.80   3.496%   $125.0232   $125.02   $125.00   $125.00  
  Purchase #5 $239.94   9.701%   $263.2166   $263.22   $263.20   $263.20  
  Purchase #6 $130.96   10.123%   $144.2171   $144.22   $144.20   $144.20  
  Purchase #7 $23.56   5.113%   $24.7646   $24.76   $24.75   $24.80  
  7 purchase totals = $1,068.98       $1,161.8984   $1,161.89   $1,161.85   $1,161.80