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 $168.51   6.562%   $179.5676   $179.57   $179.55   $179.60  
  Purchase #2 $112.58   10.441%   $124.3345   $124.33   $124.35   $124.30  
  Purchase #3 $223.52   11.642%   $249.5422   $249.54   $249.55   $249.50  
  Purchase #4 $49.82   7.557%   $53.5849   $53.58   $53.60   $53.60  
  Purchase #5 $92.85   4.546%   $97.071   $97.07   $97.05   $97.10  
  Purchase #6 $23.35   4.332%   $24.3615   $24.36   $24.35   $24.40  
  Purchase #7 $25.67   5.173%   $26.9979   $27.00   $27.00   $27.00  
  7 purchase totals = $696.30       $755.4596   $755.45   $755.45   $755.50