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 $67.48   4.205%   $70.3175   $70.32   $70.30   $70.30  
  Purchase #2 $224.84   11.699%   $251.144   $251.14   $251.15   $251.10  
  Purchase #3 $44.59   8.734%   $48.4845   $48.48   $48.50   $48.50  
  Purchase #4 $222.59   5.834%   $235.5759   $235.58   $235.60   $235.60  
  Purchase #5 $178.82   12.578%   $201.312   $201.31   $201.30   $201.30  
  Purchase #6 $217.44   12.201%   $243.9699   $243.97   $243.95   $244.00  
  Purchase #7 $93.28   4.394%   $97.3787   $97.38   $97.40   $97.40  
  7 purchase totals = $1,049.04       $1,148.1825   $1,148.18   $1,148.20   $1,148.20