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 $83.42   12.377%   $93.7449   $93.74   $93.75   $93.70  
  Purchase #2 $187.66   3.740%   $194.6785   $194.68   $194.70   $194.70  
  Purchase #3 $205.60   13.551%   $233.4609   $233.46   $233.45   $233.50  
  Purchase #4 $152.93   11.814%   $170.9972   $171.00   $171.00   $171.00  
  Purchase #5 $233.30   4.599%   $244.0295   $244.03   $244.05   $244.00  
  Purchase #6 $11.53   12.287%   $12.9467   $12.95   $12.95   $12.90  
  Purchase #7 $76.65   10.594%   $84.7703   $84.77   $84.75   $84.80  
  7 purchase totals = $951.09       $1,034.6280   $1,034.63   $1,034.65   $1,034.60