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 $41.94   7.311%   $45.0062   $45.01   $45.00   $45.00  
  Purchase #2 $221.31   9.232%   $241.7413   $241.74   $241.75   $241.70  
  Purchase #3 $128.86   3.228%   $133.0196   $133.02   $133.00   $133.00  
  Purchase #4 $151.67   6.847%   $162.0548   $162.05   $162.05   $162.10  
  Purchase #5 $132.31   8.855%   $144.0261   $144.03   $144.05   $144.00  
  Purchase #6 $235.40   6.412%   $250.4938   $250.49   $250.50   $250.50  
  Purchase #7 $167.54   4.439%   $174.9771   $174.98   $175.00   $175.00  
  7 purchase totals = $1,079.03       $1,151.3189   $1,151.32   $1,151.35   $1,151.30