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 $105.94   9.197%   $115.6833   $115.68   $115.70   $115.70  
  Purchase #2 $59.31   10.680%   $65.6443   $65.64   $65.65   $65.60  
  Purchase #3 $27.56   12.847%   $31.1006   $31.10   $31.10   $31.10  
  Purchase #4 $118.49   8.301%   $128.3259   $128.33   $128.35   $128.30  
  Purchase #5 $218.59   6.589%   $232.9929   $232.99   $233.00   $233.00  
  Purchase #6 $216.28   11.599%   $241.3663   $241.37   $241.35   $241.40  
  Purchase #7 $96.58   8.178%   $104.4783   $104.48   $104.50   $104.50  
  7 purchase totals = $842.75       $919.5916   $919.59   $919.65   $919.60