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 $207.69   8.325%   $224.9802   $224.98   $225.00   $225.00  
  Purchase #2 $65.42   6.258%   $69.514   $69.51   $69.50   $69.50  
  Purchase #3 $245.73   12.136%   $275.5518   $275.55   $275.55   $275.60  
  Purchase #4 $41.93   9.242%   $45.8052   $45.81   $45.80   $45.80  
  Purchase #5 $44.95   5.718%   $47.5202   $47.52   $47.50   $47.50  
  Purchase #6 $196.98   10.768%   $218.1908   $218.19   $218.20   $218.20  
  Purchase #7 $110.77   13.115%   $125.2975   $125.30   $125.30   $125.30  
  7 purchase totals = $913.47       $1,006.8597   $1,006.86   $1,006.85   $1,006.90