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 $213.92   4.251%   $223.0137   $223.01   $223.00   $223.00  
  Purchase #2 $124.65   11.222%   $138.6382   $138.64   $138.65   $138.60  
  Purchase #3 $218.46   9.549%   $239.3207   $239.32   $239.30   $239.30  
  Purchase #4 $79.78   7.300%   $85.6039   $85.60   $85.60   $85.60  
  Purchase #5 $224.71   13.428%   $254.8841   $254.88   $254.90   $254.90  
  Purchase #6 $235.26   12.680%   $265.091   $265.09   $265.10   $265.10  
  Purchase #7 $164.45   3.755%   $170.6251   $170.63   $170.65   $170.60  
  7 purchase totals = $1,261.23       $1,377.1767   $1,377.17   $1,377.20   $1,377.10