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 $60.92   7.403%   $65.4299   $65.43   $65.45   $65.40  
  Purchase #2 $160.76   6.263%   $170.8284   $170.83   $170.85   $170.80  
  Purchase #3 $219.60   9.675%   $240.8463   $240.85   $240.85   $240.80  
  Purchase #4 $53.66   6.284%   $57.032   $57.03   $57.05   $57.00  
  Purchase #5 $114.65   5.731%   $121.2206   $121.22   $121.20   $121.20  
  Purchase #6 $238.83   13.543%   $271.1747   $271.17   $271.15   $271.20  
  Purchase #7 $94.66   11.678%   $105.7144   $105.71   $105.70   $105.70  
  7 purchase totals = $943.08       $1,032.2463   $1,032.24   $1,032.25   $1,032.10