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 $76.84   4.832%   $80.5529   $80.55   $80.55   $80.60  
  Purchase #2 $195.48   10.736%   $216.4667   $216.47   $216.45   $216.50  
  Purchase #3 $16.92   10.694%   $18.7294   $18.73   $18.75   $18.70  
  Purchase #4 $247.34   4.279%   $257.9237   $257.92   $257.90   $257.90  
  Purchase #5 $201.84   11.791%   $225.639   $225.64   $225.65   $225.60  
  Purchase #6 $58.64   12.863%   $66.1829   $66.18   $66.20   $66.20  
  Purchase #7 $164.91   7.454%   $177.2024   $177.20   $177.20   $177.20  
  7 purchase totals = $961.97       $1,042.6970   $1,042.69   $1,042.70   $1,042.70