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 $224.79   8.179%   $243.1756   $243.18   $243.20   $243.20  
  Purchase #2 $109.56   12.845%   $123.633   $123.63   $123.65   $123.60  
  Purchase #3 $128.30   6.337%   $136.4304   $136.43   $136.45   $136.40  
  Purchase #4 $213.55   6.658%   $227.7682   $227.77   $227.75   $227.80  
  Purchase #5 $178.81   6.620%   $190.6472   $190.65   $190.65   $190.60  
  Purchase #6 $124.35   5.424%   $131.0947   $131.09   $131.10   $131.10  
  Purchase #7 $202.74   4.159%   $211.172   $211.17   $211.15   $211.20  
  7 purchase totals = $1,182.10       $1,263.9211   $1,263.92   $1,263.95   $1,263.90