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 $88.68   8.309%   $96.0484   $96.05   $96.05   $96.00  
  Purchase #2 $70.79   8.155%   $76.5629   $76.56   $76.55   $76.60  
  Purchase #3 $25.88   4.606%   $27.072   $27.07   $27.05   $27.10  
  Purchase #4 $227.33   12.247%   $255.1711   $255.17   $255.15   $255.20  
  Purchase #5 $230.26   9.379%   $251.8561   $251.86   $251.85   $251.90  
  Purchase #6 $138.81   10.778%   $153.7709   $153.77   $153.75   $153.80  
  Purchase #7 $194.25   11.258%   $216.1187   $216.12   $216.10   $216.10  
  7 purchase totals = $976.00       $1,076.6001   $1,076.60   $1,076.50   $1,076.70