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 $69.51   6.480%   $74.0142   $74.01   $74.00   $74.00  
  Purchase #2 $180.39   13.424%   $204.6056   $204.61   $204.60   $204.60  
  Purchase #3 $172.92   11.339%   $192.5274   $192.53   $192.55   $192.50  
  Purchase #4 $242.92   7.283%   $260.6119   $260.61   $260.60   $260.60  
  Purchase #5 $153.55   13.733%   $174.637   $174.64   $174.65   $174.60  
  Purchase #6 $20.64   13.762%   $23.4805   $23.48   $23.50   $23.50  
  Purchase #7 $242.81   8.409%   $263.2279   $263.23   $263.25   $263.20  
  7 purchase totals = $1,082.74       $1,193.1045   $1,193.11   $1,193.15   $1,193.00