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 $118.86   6.396%   $126.4623   $126.46   $126.45   $126.50  
  Purchase #2 $94.96   11.532%   $105.9108   $105.91   $105.90   $105.90  
  Purchase #3 $123.53   9.445%   $135.1974   $135.20   $135.20   $135.20  
  Purchase #4 $183.43   4.821%   $192.2732   $192.27   $192.25   $192.30  
  Purchase #5 $202.55   10.764%   $224.3525   $224.35   $224.35   $224.40  
  Purchase #6 $53.99   8.643%   $58.6564   $58.66   $58.65   $58.70  
  Purchase #7 $97.64   6.523%   $104.0091   $104.01   $104.00   $104.00  
  7 purchase totals = $874.96       $946.8617   $946.86   $946.80   $947.00