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 $11.35   12.157%   $12.7298   $12.73   $12.75   $12.70  
  Purchase #2 $189.28   4.603%   $197.9926   $197.99   $198.00   $198.00  
  Purchase #3 $21.91   13.603%   $24.8904   $24.89   $24.90   $24.90  
  Purchase #4 $211.67   11.872%   $236.7995   $236.80   $236.80   $236.80  
  Purchase #5 $96.49   12.279%   $108.338   $108.34   $108.35   $108.30  
  Purchase #6 $52.55   10.584%   $58.1119   $58.11   $58.10   $58.10  
  Purchase #7 $109.61   12.332%   $123.1271   $123.13   $123.15   $123.10  
  7 purchase totals = $692.86       $761.9893   $761.99   $762.05   $761.90