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 $203.61   6.296%   $216.4293   $216.43   $216.45   $216.40  
  Purchase #2 $174.45   3.245%   $180.1109   $180.11   $180.10   $180.10  
  Purchase #3 $173.99   8.640%   $189.0227   $189.02   $189.00   $189.00  
  Purchase #4 $240.36   10.318%   $265.1603   $265.16   $265.15   $265.20  
  Purchase #5 $33.92   12.487%   $38.1556   $38.16   $38.15   $38.20  
  Purchase #6 $45.52   7.345%   $48.8634   $48.86   $48.85   $48.90  
  Purchase #7 $138.42   12.281%   $155.4194   $155.42   $155.40   $155.40  
  7 purchase totals = $1,010.27       $1,093.1616   $1,093.16   $1,093.10   $1,093.20