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 $83.47   12.142%   $93.6049   $93.60   $93.60   $93.60  
  Purchase #2 $195.77   7.313%   $210.0867   $210.09   $210.10   $210.10  
  Purchase #3 $164.63   6.823%   $175.8627   $175.86   $175.85   $175.90  
  Purchase #4 $99.59   3.190%   $102.7669   $102.77   $102.75   $102.80  
  Purchase #5 $57.68   13.695%   $65.5793   $65.58   $65.60   $65.60  
  Purchase #6 $109.61   13.801%   $124.7373   $124.74   $124.75   $124.70  
  Purchase #7 $237.39   11.181%   $263.9326   $263.93   $263.95   $263.90  
  7 purchase totals = $948.14       $1,036.5704   $1,036.57   $1,036.60   $1,036.60