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 $65.75   11.199%   $73.1133   $73.11   $73.10   $73.10  
  Purchase #2 $143.71   7.612%   $154.6492   $154.65   $154.65   $154.60  
  Purchase #3 $127.84   3.851%   $132.7631   $132.76   $132.75   $132.80  
  Purchase #4 $223.57   6.633%   $238.3994   $238.40   $238.40   $238.40  
  Purchase #5 $180.74   12.786%   $203.8494   $203.85   $203.85   $203.80  
  Purchase #6 $161.98   9.194%   $176.8724   $176.87   $176.85   $176.90  
  Purchase #7 $175.59   10.482%   $193.9953   $194.00   $194.00   $194.00  
  7 purchase totals = $1,079.18       $1,173.6421   $1,173.64   $1,173.60   $1,173.60