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 $59.31   7.166%   $63.5602   $63.56   $63.55   $63.60  
  Purchase #2 $38.84   11.827%   $43.4336   $43.43   $43.45   $43.40  
  Purchase #3 $5.50   10.584%   $6.0821   $6.08   $6.10   $6.10  
  Purchase #4 $12.96   10.804%   $14.3602   $14.36   $14.35   $14.40  
  Purchase #5 $31.57   10.688%   $34.9442   $34.94   $34.95   $34.90  
  Purchase #6 $88.68   9.572%   $97.1684   $97.17   $97.15   $97.20  
  Purchase #7 $19.56   6.117%   $20.7565   $20.76   $20.75   $20.80  
  7 purchase totals = $256.42       $280.3052   $280.30   $280.30   $280.40