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 $210.99   9.359%   $230.7366   $230.74   $230.75   $230.70  
  Purchase #2 $116.92   7.371%   $125.5382   $125.54   $125.55   $125.50  
  Purchase #3 $150.44   8.333%   $162.9762   $162.98   $163.00   $163.00  
  Purchase #4 $160.83   4.196%   $167.5784   $167.58   $167.60   $167.60  
  Purchase #5 $18.48   12.645%   $20.8168   $20.82   $20.80   $20.80  
  Purchase #6 $114.65   8.747%   $124.6784   $124.68   $124.70   $124.70  
  Purchase #7 $163.63   4.700%   $171.3206   $171.32   $171.30   $171.30  
  7 purchase totals = $935.94       $1,003.6452   $1,003.66   $1,003.70   $1,003.60