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 $65.79   11.443%   $73.3183   $73.32   $73.30   $73.30  
  Purchase #2 $75.31   13.540%   $85.507   $85.51   $85.50   $85.50  
  Purchase #3 $225.57   8.167%   $243.9923   $243.99   $244.00   $244.00  
  Purchase #4 $11.76   12.149%   $13.1887   $13.19   $13.20   $13.20  
  Purchase #5 $221.30   4.514%   $231.2895   $231.29   $231.30   $231.30  
  Purchase #6 $26.41   6.433%   $28.109   $28.11   $28.10   $28.10  
  Purchase #7 $45.27   8.679%   $49.199   $49.20   $49.20   $49.20  
  7 purchase totals = $671.41       $724.6038   $724.61   $724.60   $724.60