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 $228.61   5.713%   $241.6705   $241.67   $241.65   $241.70  
  Purchase #2 $124.31   13.364%   $140.9228   $140.92   $140.90   $140.90  
  Purchase #3 $124.54   7.278%   $133.604   $133.60   $133.60   $133.60  
  Purchase #4 $188.78   10.162%   $207.9638   $207.96   $207.95   $208.00  
  Purchase #5 $185.64   3.282%   $191.7327   $191.73   $191.75   $191.70  
  Purchase #6 $82.75   6.494%   $88.1238   $88.12   $88.10   $88.10  
  Purchase #7 $210.72   11.783%   $235.5491   $235.55   $235.55   $235.50  
  7 purchase totals = $1,145.35       $1,239.5667   $1,239.55   $1,239.50   $1,239.50