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 $62.41   13.341%   $70.7361   $70.74   $70.75   $70.70  
  Purchase #2 $25.90   3.692%   $26.8562   $26.86   $26.85   $26.90  
  Purchase #3 $63.56   8.801%   $69.1539   $69.15   $69.15   $69.20  
  Purchase #4 $131.91   11.717%   $147.3659   $147.37   $147.35   $147.40  
  Purchase #5 $182.34   5.471%   $192.3158   $192.32   $192.30   $192.30  
  Purchase #6 $203.43   6.295%   $216.2359   $216.24   $216.25   $216.20  
  Purchase #7 $90.82   3.453%   $93.956   $93.96   $93.95   $94.00  
  7 purchase totals = $760.37       $816.6198   $816.64   $816.60   $816.70