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 $173.48   11.661%   $193.7095   $193.71   $193.70   $193.70  
  Purchase #2 $244.37   9.811%   $268.3451   $268.35   $268.35   $268.30  
  Purchase #3 $244.38   13.517%   $277.4128   $277.41   $277.40   $277.40  
  Purchase #4 $58.38   4.133%   $60.7928   $60.79   $60.80   $60.80  
  Purchase #5 $5.96   13.352%   $6.7558   $6.76   $6.75   $6.80  
  Purchase #6 $230.98   13.261%   $261.6103   $261.61   $261.60   $261.60  
  Purchase #7 $18.74   3.647%   $19.4234   $19.42   $19.40   $19.40  
  7 purchase totals = $976.29       $1,088.0497   $1,088.05   $1,088.00   $1,088.00