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 $173.46   8.202%   $187.6872   $187.69   $187.70   $187.70  
  Purchase #2 $43.54   6.205%   $46.2417   $46.24   $46.25   $46.20  
  Purchase #3 $81.40   5.135%   $85.5799   $85.58   $85.60   $85.60  
  Purchase #4 $39.43   6.251%   $41.8948   $41.89   $41.90   $41.90  
  Purchase #5 $203.86   5.615%   $215.3067   $215.31   $215.30   $215.30  
  Purchase #6 $53.85   12.613%   $60.6421   $60.64   $60.65   $60.60  
  Purchase #7 $102.77   10.290%   $113.345   $113.35   $113.35   $113.30  
  7 purchase totals = $698.31       $750.6974   $750.70   $750.75   $750.60