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 $32.51   7.482%   $34.9424   $34.94   $34.95   $34.90  
  Purchase #2 $81.69   13.644%   $92.8358   $92.84   $92.85   $92.80  
  Purchase #3 $98.48   8.551%   $106.901   $106.90   $106.90   $106.90  
  Purchase #4 $123.90   6.709%   $132.2125   $132.21   $132.20   $132.20  
  Purchase #5 $181.94   6.578%   $193.908   $193.91   $193.90   $193.90  
  Purchase #6 $238.89   9.779%   $262.2511   $262.25   $262.25   $262.30  
  Purchase #7 $180.30   9.264%   $197.003   $197.00   $197.00   $197.00  
  7 purchase totals = $937.71       $1,020.0538   $1,020.05   $1,020.05   $1,020.00