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 $32.61   5.681%   $34.4626   $34.46   $34.45   $34.50  
  Purchase #2 $246.67   11.756%   $275.6685   $275.67   $275.65   $275.70  
  Purchase #3 $143.39   8.141%   $155.0634   $155.06   $155.05   $155.10  
  Purchase #4 $192.40   3.365%   $198.8743   $198.87   $198.85   $198.90  
  Purchase #5 $203.79   10.392%   $224.9679   $224.97   $224.95   $225.00  
  Purchase #6 $216.36   7.137%   $231.8016   $231.80   $231.80   $231.80  
  Purchase #7 $91.33   5.305%   $96.1751   $96.18   $96.20   $96.20  
  7 purchase totals = $1,126.55       $1,217.0134   $1,217.01   $1,216.95   $1,217.20