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 $50.74   4.783%   $53.1669   $53.17   $53.15   $53.20  
  Purchase #2 $195.81   5.207%   $206.0058   $206.01   $206.00   $206.00  
  Purchase #3 $161.43   12.297%   $181.281   $181.28   $181.30   $181.30  
  Purchase #4 $43.52   5.165%   $45.7678   $45.77   $45.75   $45.80  
  Purchase #5 $179.47   5.491%   $189.3247   $189.32   $189.30   $189.30  
  Purchase #6 $183.35   10.817%   $203.183   $203.18   $203.20   $203.20  
  Purchase #7 $119.33   6.427%   $126.9993   $127.00   $127.00   $127.00  
  7 purchase totals = $933.65       $1,005.7285   $1,005.73   $1,005.70   $1,005.80