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 $64.50   9.369%   $70.543   $70.54   $70.55   $70.50  
  Purchase #2 $156.40   9.392%   $171.0891   $171.09   $171.10   $171.10  
  Purchase #3 $148.84   7.788%   $160.4317   $160.43   $160.45   $160.40  
  Purchase #4 $112.88   6.677%   $120.417   $120.42   $120.40   $120.40  
  Purchase #5 $66.29   10.249%   $73.0841   $73.08   $73.10   $73.10  
  Purchase #6 $25.88   9.504%   $28.3396   $28.34   $28.35   $28.30  
  Purchase #7 $9.90   4.311%   $10.3268   $10.33   $10.35   $10.30  
  7 purchase totals = $584.69       $634.2313   $634.23   $634.30   $634.10