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 $87.95   5.436%   $92.731   $92.73   $92.75   $92.70  
  Purchase #2 $85.44   3.236%   $88.2048   $88.20   $88.20   $88.20  
  Purchase #3 $227.91   8.541%   $247.3758   $247.38   $247.40   $247.40  
  Purchase #4 $236.75   8.409%   $256.6583   $256.66   $256.65   $256.70  
  Purchase #5 $189.96   3.343%   $196.3104   $196.31   $196.30   $196.30  
  Purchase #6 $174.75   6.580%   $186.2486   $186.25   $186.25   $186.20  
  Purchase #7 $75.76   9.621%   $83.0489   $83.05   $83.05   $83.00  
  7 purchase totals = $1,078.52       $1,150.5778   $1,150.58   $1,150.60   $1,150.50