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 $54.46   8.224%   $58.9388   $58.94   $58.95   $58.90  
  Purchase #2 $185.29   9.740%   $203.3372   $203.34   $203.35   $203.30  
  Purchase #3 $54.70   5.511%   $57.7145   $57.71   $57.70   $57.70  
  Purchase #4 $205.89   5.126%   $216.4439   $216.44   $216.45   $216.40  
  Purchase #5 $76.25   11.236%   $84.8175   $84.82   $84.80   $84.80  
  Purchase #6 $64.85   6.432%   $69.0212   $69.02   $69.00   $69.00  
  Purchase #7 $64.32   4.830%   $67.4267   $67.43   $67.45   $67.40  
  7 purchase totals = $705.76       $757.6998   $757.70   $757.70   $757.50