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 $171.45   12.598%   $193.0493   $193.05   $193.05   $193.00  
  Purchase #2 $245.82   12.354%   $276.1886   $276.19   $276.20   $276.20  
  Purchase #3 $154.98   7.126%   $166.0239   $166.02   $166.00   $166.00  
  Purchase #4 $81.59   8.210%   $88.2885   $88.29   $88.30   $88.30  
  Purchase #5 $190.94   7.113%   $204.5216   $204.52   $204.50   $204.50  
  Purchase #6 $68.37   7.519%   $73.5107   $73.51   $73.50   $73.50  
  Purchase #7 $241.91   10.581%   $267.5065   $267.51   $267.50   $267.50  
  7 purchase totals = $1,155.06       $1,269.0891   $1,269.09   $1,269.05   $1,269.00