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 $60.59   11.337%   $67.4591   $67.46   $67.45   $67.50  
  Purchase #2 $234.66   7.823%   $253.0175   $253.02   $253.00   $253.00  
  Purchase #3 $189.97   7.287%   $203.8131   $203.81   $203.80   $203.80  
  Purchase #4 $220.84   9.334%   $241.4532   $241.45   $241.45   $241.50  
  Purchase #5 $24.87   13.593%   $28.2506   $28.25   $28.25   $28.30  
  Purchase #6 $54.45   7.780%   $58.6862   $58.69   $58.70   $58.70  
  Purchase #7 $13.79   8.784%   $15.0013   $15.00   $15.00   $15.00  
  7 purchase totals = $799.17       $867.6810   $867.68   $867.65   $867.80