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 $187.46   7.211%   $200.9777   $200.98   $201.00   $201.00  
  Purchase #2 $219.25   12.616%   $246.9106   $246.91   $246.90   $246.90  
  Purchase #3 $37.87   4.531%   $39.5859   $39.59   $39.60   $39.60  
  Purchase #4 $69.86   7.522%   $75.1149   $75.11   $75.10   $75.10  
  Purchase #5 $240.49   5.352%   $253.361   $253.36   $253.35   $253.40  
  Purchase #6 $200.90   6.138%   $213.2312   $213.23   $213.25   $213.20  
  Purchase #7 $181.25   11.443%   $201.9904   $201.99   $202.00   $202.00  
  7 purchase totals = $1,137.08       $1,231.1717   $1,231.17   $1,231.20   $1,231.20