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 $60.75   13.154%   $68.7411   $68.74   $68.75   $68.70  
  Purchase #2 $237.65   5.460%   $250.6257   $250.63   $250.65   $250.60  
  Purchase #3 $112.37   8.245%   $121.6349   $121.63   $121.65   $121.60  
  Purchase #4 $210.35   4.293%   $219.3803   $219.38   $219.40   $219.40  
  Purchase #5 $23.74   11.860%   $26.5556   $26.56   $26.55   $26.60  
  Purchase #6 $80.82   8.679%   $87.8344   $87.83   $87.85   $87.80  
  Purchase #7 $227.90   5.565%   $240.5826   $240.58   $240.60   $240.60  
  7 purchase totals = $953.58       $1,015.3546   $1,015.35   $1,015.45   $1,015.30