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 $23.94   3.763%   $24.8409   $24.84   $24.85   $24.80  
  Purchase #2 $172.40   6.778%   $184.0853   $184.09   $184.10   $184.10  
  Purchase #3 $115.63   11.393%   $128.8037   $128.80   $128.80   $128.80  
  Purchase #4 $102.52   3.727%   $106.3409   $106.34   $106.35   $106.30  
  Purchase #5 $218.28   8.560%   $236.9648   $236.96   $236.95   $237.00  
  Purchase #6 $238.31   11.513%   $265.7466   $265.75   $265.75   $265.70  
  Purchase #7 $206.45   9.716%   $226.5087   $226.51   $226.50   $226.50  
  7 purchase totals = $1,077.53       $1,173.2909   $1,173.29   $1,173.30   $1,173.20