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 $126.70   11.497%   $141.2667   $141.27   $141.25   $141.30  
  Purchase #2 $165.92   11.116%   $184.3637   $184.36   $184.35   $184.40  
  Purchase #3 $241.77   12.166%   $271.1837   $271.18   $271.20   $271.20  
  Purchase #4 $96.97   9.867%   $106.538   $106.54   $106.55   $106.50  
  Purchase #5 $158.72   11.122%   $176.3728   $176.37   $176.35   $176.40  
  Purchase #6 $6.79   3.294%   $7.0137   $7.01   $7.00   $7.00  
  Purchase #7 $129.36   6.709%   $138.0388   $138.04   $138.05   $138.00  
  7 purchase totals = $926.23       $1,024.7774   $1,024.77   $1,024.75   $1,024.80