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 $165.94   11.325%   $184.7327   $184.73   $184.75   $184.70  
  Purchase #2 $60.67   5.349%   $63.9152   $63.92   $63.90   $63.90  
  Purchase #3 $239.39   7.395%   $257.0929   $257.09   $257.10   $257.10  
  Purchase #4 $239.26   9.699%   $262.4658   $262.47   $262.45   $262.50  
  Purchase #5 $93.51   5.848%   $98.9785   $98.98   $99.00   $99.00  
  Purchase #6 $169.65   12.840%   $191.4331   $191.43   $191.45   $191.40  
  Purchase #7 $190.60   7.118%   $204.1669   $204.17   $204.15   $204.20  
  7 purchase totals = $1,159.02       $1,262.7851   $1,262.79   $1,262.80   $1,262.80