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 $103.64   11.422%   $115.4778   $115.48   $115.50   $115.50  
  Purchase #2 $238.31   6.312%   $253.3521   $253.35   $253.35   $253.40  
  Purchase #3 $173.56   6.417%   $184.6973   $184.70   $184.70   $184.70  
  Purchase #4 $219.44   7.184%   $235.2046   $235.20   $235.20   $235.20  
  Purchase #5 $208.97   8.293%   $226.2999   $226.30   $226.30   $226.30  
  Purchase #6 $62.99   3.502%   $65.1959   $65.20   $65.20   $65.20  
  Purchase #7 $172.52   10.429%   $190.5121   $190.51   $190.50   $190.50  
  7 purchase totals = $1,179.43       $1,270.7397   $1,270.74   $1,270.75   $1,270.80