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 $62.96   10.608%   $69.6388   $69.64   $69.65   $69.60  
  Purchase #2 $179.50   3.421%   $185.6407   $185.64   $185.65   $185.60  
  Purchase #3 $212.33   7.509%   $228.2739   $228.27   $228.25   $228.30  
  Purchase #4 $243.98   7.449%   $262.1541   $262.15   $262.15   $262.20  
  Purchase #5 $133.53   11.776%   $149.2545   $149.25   $149.25   $149.30  
  Purchase #6 $105.26   10.489%   $116.3007   $116.30   $116.30   $116.30  
  Purchase #7 $44.43   4.179%   $46.2867   $46.29   $46.30   $46.30  
  7 purchase totals = $981.99       $1,057.5494   $1,057.54   $1,057.55   $1,057.60