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 $85.40   12.764%   $96.3005   $96.30   $96.30   $96.30  
  Purchase #2 $113.76   11.705%   $127.0756   $127.08   $127.10   $127.10  
  Purchase #3 $176.79   9.800%   $194.1154   $194.12   $194.10   $194.10  
  Purchase #4 $44.37   10.145%   $48.8713   $48.87   $48.85   $48.90  
  Purchase #5 $144.80   8.774%   $157.5048   $157.50   $157.50   $157.50  
  Purchase #6 $33.65   11.133%   $37.3963   $37.40   $37.40   $37.40  
  Purchase #7 $141.91   10.479%   $156.7807   $156.78   $156.80   $156.80  
  7 purchase totals = $740.68       $818.0446   $818.05   $818.05   $818.10