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 $49.48   7.596%   $53.2385   $53.24   $53.25   $53.20  
  Purchase #2 $227.65   3.335%   $235.2421   $235.24   $235.25   $235.20  
  Purchase #3 $219.53   11.510%   $244.7979   $244.80   $244.80   $244.80  
  Purchase #4 $33.94   10.653%   $37.5556   $37.56   $37.55   $37.60  
  Purchase #5 $205.70   12.351%   $231.106   $231.11   $231.10   $231.10  
  Purchase #6 $188.91   12.731%   $212.9601   $212.96   $212.95   $213.00  
  Purchase #7 $200.95   5.150%   $211.2989   $211.30   $211.30   $211.30  
  7 purchase totals = $1,126.16       $1,226.1991   $1,226.21   $1,226.20   $1,226.20