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 $62.68   3.767%   $65.0412   $65.04   $65.05   $65.00  
  Purchase #2 $65.89   13.436%   $74.743   $74.74   $74.75   $74.70  
  Purchase #3 $94.99   3.146%   $97.9784   $97.98   $98.00   $98.00  
  Purchase #4 $124.72   11.701%   $139.3135   $139.31   $139.30   $139.30  
  Purchase #5 $144.83   11.263%   $161.1422   $161.14   $161.15   $161.10  
  Purchase #6 $246.80   13.414%   $279.9058   $279.91   $279.90   $279.90  
  Purchase #7 $5.43   11.583%   $6.059   $6.06   $6.05   $6.10  
  7 purchase totals = $745.34       $824.1831   $824.18   $824.20   $824.10