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 $68.65   12.151%   $76.9917   $76.99   $77.00   $77.00  
  Purchase #2 $245.91   12.410%   $276.4274   $276.43   $276.45   $276.40  
  Purchase #3 $110.33   11.203%   $122.6903   $122.69   $122.70   $122.70  
  Purchase #4 $216.32   8.327%   $234.333   $234.33   $234.35   $234.30  
  Purchase #5 $47.73   4.461%   $49.8592   $49.86   $49.85   $49.90  
  Purchase #6 $84.38   11.654%   $94.2136   $94.21   $94.20   $94.20  
  Purchase #7 $201.84   11.711%   $225.4775   $225.48   $225.50   $225.50  
  7 purchase totals = $975.16       $1,079.9927   $1,079.99   $1,080.05   $1,080.00