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 $109.47   13.802%   $124.579   $124.58   $124.60   $124.60  
  Purchase #2 $71.41   8.809%   $77.7005   $77.70   $77.70   $77.70  
  Purchase #3 $172.91   8.407%   $187.4465   $187.45   $187.45   $187.40  
  Purchase #4 $141.43   8.716%   $153.757   $153.76   $153.75   $153.80  
  Purchase #5 $39.48   6.751%   $42.1453   $42.15   $42.15   $42.10  
  Purchase #6 $216.45   8.819%   $235.5387   $235.54   $235.55   $235.50  
  Purchase #7 $183.91   9.717%   $201.7805   $201.78   $201.80   $201.80  
  7 purchase totals = $935.06       $1,022.9475   $1,022.96   $1,023.00   $1,022.90