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 $172.86   11.794%   $193.2471   $193.25   $193.25   $193.20  
  Purchase #2 $238.35   10.274%   $262.8381   $262.84   $262.85   $262.80  
  Purchase #3 $152.48   9.661%   $167.2111   $167.21   $167.20   $167.20  
  Purchase #4 $27.89   8.663%   $30.3061   $30.31   $30.30   $30.30  
  Purchase #5 $45.35   9.858%   $49.8206   $49.82   $49.80   $49.80  
  Purchase #6 $119.85   9.632%   $131.394   $131.39   $131.40   $131.40  
  Purchase #7 $169.63   9.805%   $186.2622   $186.26   $186.25   $186.30  
  7 purchase totals = $926.41       $1,021.0792   $1,021.08   $1,021.05   $1,021.00