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 $53.58   12.617%   $60.3402   $60.34   $60.35   $60.30  
  Purchase #2 $214.95   5.260%   $226.2564   $226.26   $226.25   $226.30  
  Purchase #3 $181.72   11.381%   $202.4016   $202.40   $202.40   $202.40  
  Purchase #4 $100.94   3.263%   $104.2337   $104.23   $104.25   $104.20  
  Purchase #5 $219.40   9.530%   $240.3088   $240.31   $240.30   $240.30  
  Purchase #6 $29.88   6.277%   $31.7556   $31.76   $31.75   $31.80  
  Purchase #7 $85.59   4.462%   $89.409   $89.41   $89.40   $89.40  
  7 purchase totals = $886.06       $954.7053   $954.71   $954.70   $954.70