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 $56.92   7.561%   $61.2237   $61.22   $61.20   $61.20  
  Purchase #2 $215.38   7.405%   $231.3289   $231.33   $231.35   $231.30  
  Purchase #3 $68.33   11.164%   $75.9584   $75.96   $75.95   $76.00  
  Purchase #4 $175.96   13.496%   $199.7076   $199.71   $199.70   $199.70  
  Purchase #5 $235.63   11.751%   $263.3189   $263.32   $263.30   $263.30  
  Purchase #6 $149.52   8.538%   $162.286   $162.29   $162.30   $162.30  
  Purchase #7 $77.80   4.735%   $81.4838   $81.48   $81.50   $81.50  
  7 purchase totals = $979.54       $1,075.3073   $1,075.31   $1,075.30   $1,075.30