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 $24.66   3.736%   $25.5813   $25.58   $25.60   $25.60  
  Purchase #2 $135.48   6.839%   $144.7455   $144.75   $144.75   $144.70  
  Purchase #3 $213.64   8.683%   $232.1904   $232.19   $232.20   $232.20  
  Purchase #4 $83.82   9.273%   $91.5926   $91.59   $91.60   $91.60  
  Purchase #5 $180.38   9.322%   $197.195   $197.20   $197.20   $197.20  
  Purchase #6 $235.38   4.667%   $246.3652   $246.37   $246.35   $246.40  
  Purchase #7 $119.70   10.868%   $132.709   $132.71   $132.70   $132.70  
  7 purchase totals = $993.06       $1,070.3790   $1,070.39   $1,070.40   $1,070.40