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 $62.87   3.286%   $64.9359   $64.94   $64.95   $64.90  
  Purchase #2 $179.48   12.753%   $202.3691   $202.37   $202.35   $202.40  
  Purchase #3 $23.51   12.820%   $26.524   $26.52   $26.50   $26.50  
  Purchase #4 $38.65   3.309%   $39.9289   $39.93   $39.95   $39.90  
  Purchase #5 $194.31   7.433%   $208.7531   $208.75   $208.75   $208.80  
  Purchase #6 $201.59   9.397%   $220.5334   $220.53   $220.55   $220.50  
  Purchase #7 $43.92   9.650%   $48.1583   $48.16   $48.15   $48.20  
  7 purchase totals = $744.33       $811.2027   $811.20   $811.20   $811.20