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 $31.98   6.177%   $33.9554   $33.96   $33.95   $34.00  
  Purchase #2 $59.72   11.654%   $66.6798   $66.68   $66.70   $66.70  
  Purchase #3 $207.55   7.454%   $223.0208   $223.02   $223.00   $223.00  
  Purchase #4 $26.96   7.319%   $28.9332   $28.93   $28.95   $28.90  
  Purchase #5 $15.33   7.565%   $16.4897   $16.49   $16.50   $16.50  
  Purchase #6 $21.86   9.703%   $23.9811   $23.98   $24.00   $24.00  
  Purchase #7 $216.98   7.429%   $233.0994   $233.10   $233.10   $233.10  
  7 purchase totals = $580.38       $626.1594   $626.16   $626.20   $626.20