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 $149.63   9.143%   $163.3107   $163.31   $163.30   $163.30  
  Purchase #2 $167.56   6.628%   $178.6659   $178.67   $178.65   $178.70  
  Purchase #3 $194.55   11.775%   $217.4583   $217.46   $217.45   $217.50  
  Purchase #4 $95.46   7.436%   $102.5584   $102.56   $102.55   $102.60  
  Purchase #5 $151.48   8.772%   $164.7678   $164.77   $164.75   $164.80  
  Purchase #6 $235.36   4.597%   $246.1795   $246.18   $246.20   $246.20  
  Purchase #7 $187.33   6.575%   $199.6469   $199.65   $199.65   $199.60  
  7 purchase totals = $1,181.37       $1,272.5875   $1,272.60   $1,272.55   $1,272.70