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 $189.86   8.290%   $205.5994   $205.60   $205.60   $205.60  
  Purchase #2 $165.80   10.759%   $183.6384   $183.64   $183.65   $183.60  
  Purchase #3 $159.72   6.667%   $170.3685   $170.37   $170.35   $170.40  
  Purchase #4 $87.58   4.714%   $91.7085   $91.71   $91.70   $91.70  
  Purchase #5 $207.55   10.652%   $229.6582   $229.66   $229.65   $229.70  
  Purchase #6 $216.43   13.799%   $246.2952   $246.30   $246.30   $246.30  
  Purchase #7 $156.60   4.131%   $163.0691   $163.07   $163.05   $163.10  
  7 purchase totals = $1,183.54       $1,290.3373   $1,290.35   $1,290.30   $1,290.40