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 $33.67   4.818%   $35.2922   $35.29   $35.30   $35.30  
  Purchase #2 $228.98   7.591%   $246.3619   $246.36   $246.35   $246.40  
  Purchase #3 $156.58   11.572%   $174.6994   $174.70   $174.70   $174.70  
  Purchase #4 $195.76   9.528%   $214.412   $214.41   $214.40   $214.40  
  Purchase #5 $200.58   12.614%   $225.8812   $225.88   $225.90   $225.90  
  Purchase #6 $191.68   6.732%   $204.5839   $204.58   $204.60   $204.60  
  Purchase #7 $166.68   8.795%   $181.3395   $181.34   $181.35   $181.30  
  7 purchase totals = $1,173.93       $1,282.5701   $1,282.56   $1,282.60   $1,282.60