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 $41.41   6.210%   $43.9816   $43.98   $44.00   $44.00  
  Purchase #2 $182.67   11.216%   $203.1583   $203.16   $203.15   $203.20  
  Purchase #3 $156.35   7.696%   $168.3827   $168.38   $168.40   $168.40  
  Purchase #4 $202.74   11.261%   $225.5706   $225.57   $225.55   $225.60  
  Purchase #5 $247.85   6.415%   $263.7496   $263.75   $263.75   $263.70  
  Purchase #6 $57.36   5.523%   $60.528   $60.53   $60.55   $60.50  
  Purchase #7 $8.58   6.624%   $9.1483   $9.15   $9.15   $9.10  
  7 purchase totals = $896.96       $974.5191   $974.52   $974.55   $974.50