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 $50.26   11.519%   $56.0494   $56.05   $56.05   $56.00  
  Purchase #2 $96.85   6.194%   $102.8489   $102.85   $102.85   $102.80  
  Purchase #3 $59.57   5.741%   $62.9899   $62.99   $63.00   $63.00  
  Purchase #4 $203.68   7.824%   $219.6159   $219.62   $219.60   $219.60  
  Purchase #5 $55.85   11.868%   $62.4783   $62.48   $62.50   $62.50  
  Purchase #6 $220.98   5.612%   $233.3814   $233.38   $233.40   $233.40  
  Purchase #7 $239.83   12.787%   $270.4971   $270.50   $270.50   $270.50  
  7 purchase totals = $927.02       $1,007.8609   $1,007.87   $1,007.90   $1,007.80