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 $126.79   5.870%   $134.2326   $134.23   $134.25   $134.20  
  Purchase #2 $248.27   12.313%   $278.8395   $278.84   $278.85   $278.80  
  Purchase #3 $239.93   10.339%   $264.7364   $264.74   $264.75   $264.70  
  Purchase #4 $64.39   4.496%   $67.285   $67.29   $67.30   $67.30  
  Purchase #5 $56.41   10.447%   $62.3032   $62.30   $62.30   $62.30  
  Purchase #6 $169.58   13.556%   $192.5683   $192.57   $192.55   $192.60  
  Purchase #7 $235.88   3.689%   $244.5816   $244.58   $244.60   $244.60  
  7 purchase totals = $1,141.25       $1,244.5466   $1,244.55   $1,244.60   $1,244.50