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 $171.56   13.504%   $194.7275   $194.73   $194.75   $194.70  
  Purchase #2 $8.51   7.569%   $9.1541   $9.15   $9.15   $9.20  
  Purchase #3 $107.59   9.161%   $117.4463   $117.45   $117.45   $117.40  
  Purchase #4 $68.49   9.448%   $74.9609   $74.96   $74.95   $75.00  
  Purchase #5 $216.52   11.515%   $241.4523   $241.45   $241.45   $241.50  
  Purchase #6 $131.63   3.801%   $136.6333   $136.63   $136.65   $136.60  
  Purchase #7 $20.75   13.820%   $23.6177   $23.62   $23.60   $23.60  
  7 purchase totals = $725.05       $797.9921   $797.99   $798.00   $798.00