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 $184.35   5.856%   $195.1455   $195.15   $195.15   $195.10  
  Purchase #2 $240.75   6.765%   $257.0367   $257.04   $257.05   $257.00  
  Purchase #3 $133.57   13.607%   $151.7449   $151.74   $151.75   $151.70  
  Purchase #4 $61.82   8.398%   $67.0116   $67.01   $67.00   $67.00  
  Purchase #5 $108.56   7.123%   $116.2927   $116.29   $116.30   $116.30  
  Purchase #6 $50.67   9.774%   $55.6225   $55.62   $55.60   $55.60  
  Purchase #7 $60.55   13.170%   $68.5244   $68.52   $68.50   $68.50  
  7 purchase totals = $840.27       $911.3783   $911.37   $911.35   $911.20