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 $160.47   6.165%   $170.363   $170.36   $170.35   $170.40  
  Purchase #2 $67.75   10.362%   $74.7703   $74.77   $74.75   $74.80  
  Purchase #3 $124.37   13.795%   $141.5268   $141.53   $141.55   $141.50  
  Purchase #4 $214.59   13.829%   $244.2657   $244.27   $244.25   $244.30  
  Purchase #5 $59.60   8.129%   $64.4449   $64.44   $64.45   $64.40  
  Purchase #6 $181.35   8.583%   $196.9153   $196.92   $196.90   $196.90  
  Purchase #7 $168.82   13.739%   $192.0142   $192.01   $192.00   $192.00  
  7 purchase totals = $976.95       $1,084.3002   $1,084.30   $1,084.25   $1,084.30