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 $169.50   8.304%   $183.5753   $183.58   $183.60   $183.60  
  Purchase #2 $156.56   11.553%   $174.6474   $174.65   $174.65   $174.60  
  Purchase #3 $113.80   4.821%   $119.2863   $119.29   $119.30   $119.30  
  Purchase #4 $159.87   8.858%   $174.0313   $174.03   $174.05   $174.00  
  Purchase #5 $182.75   6.599%   $194.8097   $194.81   $194.80   $194.80  
  Purchase #6 $56.64   3.858%   $58.8252   $58.83   $58.85   $58.80  
  Purchase #7 $229.49   10.731%   $254.1166   $254.12   $254.10   $254.10  
  7 purchase totals = $1,068.61       $1,159.2918   $1,159.31   $1,159.35   $1,159.20