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 $208.82   9.310%   $228.2611   $228.26   $228.25   $228.30  
  Purchase #2 $183.94   10.446%   $203.1544   $203.15   $203.15   $203.20  
  Purchase #3 $24.98   12.804%   $28.1784   $28.18   $28.20   $28.20  
  Purchase #4 $181.36   7.274%   $194.5521   $194.55   $194.55   $194.60  
  Purchase #5 $154.99   6.388%   $164.8908   $164.89   $164.90   $164.90  
  Purchase #6 $228.30   7.845%   $246.2101   $246.21   $246.20   $246.20  
  Purchase #7 $129.36   8.470%   $140.3168   $140.32   $140.30   $140.30  
  7 purchase totals = $1,111.75       $1,205.5637   $1,205.56   $1,205.55   $1,205.70