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 $184.53   9.487%   $202.0364   $202.04   $202.05   $202.00  
  Purchase #2 $60.83   9.684%   $66.7208   $66.72   $66.70   $66.70  
  Purchase #3 $7.75   8.768%   $8.4295   $8.43   $8.45   $8.40  
  Purchase #4 $198.78   11.444%   $221.5284   $221.53   $221.55   $221.50  
  Purchase #5 $54.86   7.582%   $59.0195   $59.02   $59.00   $59.00  
  Purchase #6 $210.55   6.208%   $223.6209   $223.62   $223.60   $223.60  
  Purchase #7 $130.96   7.839%   $141.226   $141.23   $141.25   $141.20  
  7 purchase totals = $848.26       $922.5815   $922.59   $922.60   $922.40