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 $84.83   10.436%   $93.6829   $93.68   $93.70   $93.70  
  Purchase #2 $23.63   6.402%   $25.1428   $25.14   $25.15   $25.10  
  Purchase #3 $180.79   4.634%   $189.1678   $189.17   $189.15   $189.20  
  Purchase #4 $24.30   6.142%   $25.7925   $25.79   $25.80   $25.80  
  Purchase #5 $31.77   5.661%   $33.5685   $33.57   $33.55   $33.60  
  Purchase #6 $64.45   13.858%   $73.3815   $73.38   $73.40   $73.40  
  Purchase #7 $22.41   7.507%   $24.0923   $24.09   $24.10   $24.10  
  7 purchase totals = $432.18       $464.8283   $464.82   $464.85   $464.90