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 $124.26   10.582%   $137.4092   $137.41   $137.40   $137.40  
  Purchase #2 $88.25   7.177%   $94.5837   $94.58   $94.60   $94.60  
  Purchase #3 $161.59   8.152%   $174.7628   $174.76   $174.75   $174.80  
  Purchase #4 $202.64   9.840%   $222.5798   $222.58   $222.60   $222.60  
  Purchase #5 $107.75   5.426%   $113.5965   $113.60   $113.60   $113.60  
  Purchase #6 $133.37   7.413%   $143.2567   $143.26   $143.25   $143.30  
  Purchase #7 $100.79   11.267%   $112.146   $112.15   $112.15   $112.10  
  7 purchase totals = $918.65       $998.3347   $998.34   $998.35   $998.40