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 $61.57   10.499%   $68.0342   $68.03   $68.05   $68.00  
  Purchase #2 $60.89   6.684%   $64.9599   $64.96   $64.95   $65.00  
  Purchase #3 $160.72   10.641%   $177.8222   $177.82   $177.80   $177.80  
  Purchase #4 $187.98   10.614%   $207.9322   $207.93   $207.95   $207.90  
  Purchase #5 $91.69   9.469%   $100.3721   $100.37   $100.35   $100.40  
  Purchase #6 $5.66   4.467%   $5.9128   $5.91   $5.90   $5.90  
  Purchase #7 $97.50   13.531%   $110.6927   $110.69   $110.70   $110.70  
  7 purchase totals = $666.01       $735.7261   $735.71   $735.70   $735.70