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 $134.99   13.852%   $153.6888   $153.69   $153.70   $153.70  
  Purchase #2 $222.62   9.849%   $244.5458   $244.55   $244.55   $244.50  
  Purchase #3 $103.91   13.809%   $118.2589   $118.26   $118.25   $118.30  
  Purchase #4 $118.69   6.598%   $126.5212   $126.52   $126.50   $126.50  
  Purchase #5 $127.58   13.736%   $145.1044   $145.10   $145.10   $145.10  
  Purchase #6 $114.80   7.414%   $123.3113   $123.31   $123.30   $123.30  
  Purchase #7 $164.60   10.447%   $181.7958   $181.80   $181.80   $181.80  
  7 purchase totals = $987.19       $1,093.2262   $1,093.23   $1,093.20   $1,093.20