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 $190.52   11.124%   $211.7134   $211.71   $211.70   $211.70  
  Purchase #2 $218.78   13.294%   $247.8646   $247.86   $247.85   $247.90  
  Purchase #3 $108.70   5.287%   $114.447   $114.45   $114.45   $114.40  
  Purchase #4 $122.95   9.391%   $134.4962   $134.50   $134.50   $134.50  
  Purchase #5 $229.25   6.711%   $244.635   $244.64   $244.65   $244.60  
  Purchase #6 $91.52   12.436%   $102.9014   $102.90   $102.90   $102.90  
  Purchase #7 $195.45   7.523%   $210.1537   $210.15   $210.15   $210.20  
  7 purchase totals = $1,157.17       $1,266.2113   $1,266.21   $1,266.20   $1,266.20