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 $65.86   13.517%   $74.7623   $74.76   $74.75   $74.80  
  Purchase #2 $145.58   8.362%   $157.7534   $157.75   $157.75   $157.80  
  Purchase #3 $76.31   9.546%   $83.5946   $83.59   $83.60   $83.60  
  Purchase #4 $122.33   3.646%   $126.7902   $126.79   $126.80   $126.80  
  Purchase #5 $212.52   6.379%   $226.0767   $226.08   $226.10   $226.10  
  Purchase #6 $86.73   5.520%   $91.5175   $91.52   $91.50   $91.50  
  Purchase #7 $20.40   10.570%   $22.5563   $22.56   $22.55   $22.60  
  7 purchase totals = $729.73       $783.0510   $783.05   $783.05   $783.20