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 $179.46   13.505%   $203.6961   $203.70   $203.70   $203.70  
  Purchase #2 $70.82   7.609%   $76.2087   $76.21   $76.20   $76.20  
  Purchase #3 $153.85   13.278%   $174.2782   $174.28   $174.30   $174.30  
  Purchase #4 $91.75   6.191%   $97.4302   $97.43   $97.45   $97.40  
  Purchase #5 $239.91   6.638%   $255.8352   $255.84   $255.85   $255.80  
  Purchase #6 $174.64   12.345%   $196.1993   $196.20   $196.20   $196.20  
  Purchase #7 $236.64   9.388%   $258.8558   $258.86   $258.85   $258.90  
  7 purchase totals = $1,147.07       $1,262.5035   $1,262.52   $1,262.55   $1,262.50