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 $33.87   7.247%   $36.3246   $36.32   $36.30   $36.30  
  Purchase #2 $55.30   9.782%   $60.7094   $60.71   $60.70   $60.70  
  Purchase #3 $160.25   9.816%   $175.9801   $175.98   $176.00   $176.00  
  Purchase #4 $89.42   6.204%   $94.9676   $94.97   $94.95   $95.00  
  Purchase #5 $123.44   5.142%   $129.7873   $129.79   $129.80   $129.80  
  Purchase #6 $58.72   12.330%   $65.9602   $65.96   $65.95   $66.00  
  Purchase #7 $238.50   5.728%   $252.1613   $252.16   $252.15   $252.20  
  7 purchase totals = $759.50       $815.8905   $815.89   $815.85   $816.00