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 $169.65   7.843%   $182.9556   $182.96   $182.95   $183.00  
  Purchase #2 $68.59   11.438%   $76.4353   $76.44   $76.45   $76.40  
  Purchase #3 $40.92   8.527%   $44.4092   $44.41   $44.40   $44.40  
  Purchase #4 $58.61   7.872%   $63.2238   $63.22   $63.20   $63.20  
  Purchase #5 $220.73   4.596%   $230.8748   $230.87   $230.85   $230.90  
  Purchase #6 $224.43   6.435%   $238.8721   $238.87   $238.85   $238.90  
  Purchase #7 $202.54   5.176%   $213.0235   $213.02   $213.00   $213.00  
  7 purchase totals = $985.47       $1,049.7943   $1,049.79   $1,049.70   $1,049.80