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 $228.82   10.654%   $253.1985   $253.20   $253.20   $253.20  
  Purchase #2 $89.77   12.466%   $100.9607   $100.96   $100.95   $101.00  
  Purchase #3 $95.62   7.551%   $102.8403   $102.84   $102.85   $102.80  
  Purchase #4 $51.59   4.695%   $54.0122   $54.01   $54.00   $54.00  
  Purchase #5 $241.83   9.133%   $263.9163   $263.92   $263.90   $263.90  
  Purchase #6 $168.38   12.546%   $189.505   $189.51   $189.50   $189.50  
  Purchase #7 $137.69   8.572%   $149.4928   $149.49   $149.50   $149.50  
  7 purchase totals = $1,013.70       $1,113.9258   $1,113.93   $1,113.90   $1,113.90