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 $31.77   13.251%   $35.9798   $35.98   $36.00   $36.00  
  Purchase #2 $209.82   13.731%   $238.6304   $238.63   $238.65   $238.60  
  Purchase #3 $230.96   5.181%   $242.926   $242.93   $242.95   $242.90  
  Purchase #4 $24.69   11.124%   $27.4365   $27.44   $27.45   $27.40  
  Purchase #5 $207.64   12.598%   $233.7985   $233.80   $233.80   $233.80  
  Purchase #6 $247.71   4.588%   $259.0749   $259.07   $259.05   $259.10  
  Purchase #7 $106.37   12.777%   $119.9609   $119.96   $119.95   $120.00  
  7 purchase totals = $1,058.96       $1,157.8070   $1,157.81   $1,157.85   $1,157.80