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 $52.44   8.586%   $56.9425   $56.94   $56.95   $56.90  
  Purchase #2 $247.67   6.334%   $263.3574   $263.36   $263.35   $263.40  
  Purchase #3 $216.64   6.633%   $231.0097   $231.01   $231.00   $231.00  
  Purchase #4 $40.92   10.565%   $45.2432   $45.24   $45.25   $45.20  
  Purchase #5 $121.93   3.241%   $125.8818   $125.88   $125.90   $125.90  
  Purchase #6 $12.97   6.372%   $13.7964   $13.80   $13.80   $13.80  
  Purchase #7 $81.60   7.768%   $87.9387   $87.94   $87.95   $87.90  
  7 purchase totals = $774.17       $824.1697   $824.17   $824.20   $824.10