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 $114.56   3.313%   $118.3554   $118.36   $118.35   $118.40  
  Purchase #2 $135.75   5.759%   $143.5678   $143.57   $143.55   $143.60  
  Purchase #3 $178.97   8.166%   $193.5847   $193.58   $193.60   $193.60  
  Purchase #4 $216.56   4.289%   $225.8483   $225.85   $225.85   $225.80  
  Purchase #5 $103.26   12.192%   $115.8495   $115.85   $115.85   $115.80  
  Purchase #6 $139.75   11.630%   $156.0029   $156.00   $156.00   $156.00  
  Purchase #7 $93.45   4.493%   $97.6487   $97.65   $97.65   $97.60  
  7 purchase totals = $982.30       $1,050.8573   $1,050.86   $1,050.85   $1,050.80