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 $68.41   12.758%   $77.1377   $77.14   $77.15   $77.10  
  Purchase #2 $236.63   7.332%   $253.9797   $253.98   $254.00   $254.00  
  Purchase #3 $159.71   9.803%   $175.3664   $175.37   $175.35   $175.40  
  Purchase #4 $135.43   7.631%   $145.7647   $145.76   $145.75   $145.80  
  Purchase #5 $63.72   8.583%   $69.1891   $69.19   $69.20   $69.20  
  Purchase #6 $172.48   9.668%   $189.1554   $189.16   $189.15   $189.20  
  Purchase #7 $153.44   8.498%   $166.4793   $166.48   $166.50   $166.50  
  7 purchase totals = $989.82       $1,077.0723   $1,077.08   $1,077.10   $1,077.20