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 $91.44   11.642%   $102.0854   $102.09   $102.10   $102.10  
  Purchase #2 $218.98   4.282%   $228.3567   $228.36   $228.35   $228.40  
  Purchase #3 $222.34   8.282%   $240.7542   $240.75   $240.75   $240.80  
  Purchase #4 $156.28   10.365%   $172.4784   $172.48   $172.50   $172.50  
  Purchase #5 $230.99   12.347%   $259.5103   $259.51   $259.50   $259.50  
  Purchase #6 $65.48   11.593%   $73.0711   $73.07   $73.05   $73.10  
  Purchase #7 $122.97   10.577%   $135.9765   $135.98   $136.00   $136.00  
  7 purchase totals = $1,108.48       $1,212.2326   $1,212.24   $1,212.25   $1,212.40