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 $172.97   11.684%   $193.1798   $193.18   $193.20   $193.20  
  Purchase #2 $41.57   7.835%   $44.827   $44.83   $44.85   $44.80  
  Purchase #3 $80.68   10.733%   $89.3394   $89.34   $89.35   $89.30  
  Purchase #4 $52.64   4.485%   $55.0009   $55.00   $55.00   $55.00  
  Purchase #5 $248.74   6.231%   $264.239   $264.24   $264.25   $264.20  
  Purchase #6 $227.65   4.107%   $236.9996   $237.00   $237.00   $237.00  
  Purchase #7 $121.63   7.855%   $131.184   $131.18   $131.20   $131.20  
  7 purchase totals = $945.88       $1,014.7697   $1,014.77   $1,014.85   $1,014.70