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 $217.79   7.819%   $234.819   $234.82   $234.80   $234.80  
  Purchase #2 $211.30   13.214%   $239.2212   $239.22   $239.20   $239.20  
  Purchase #3 $50.43   4.205%   $52.5506   $52.55   $52.55   $52.60  
  Purchase #4 $212.97   5.121%   $223.8762   $223.88   $223.90   $223.90  
  Purchase #5 $178.52   8.471%   $193.6424   $193.64   $193.65   $193.60  
  Purchase #6 $163.45   8.338%   $177.0785   $177.08   $177.10   $177.10  
  Purchase #7 $131.56   3.810%   $136.5724   $136.57   $136.55   $136.60  
  7 purchase totals = $1,166.02       $1,257.7603   $1,257.76   $1,257.75   $1,257.80