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 $76.45   8.756%   $83.144   $83.14   $83.15   $83.10  
  Purchase #2 $106.79   7.492%   $114.7907   $114.79   $114.80   $114.80  
  Purchase #3 $23.48   7.137%   $25.1558   $25.16   $25.15   $25.20  
  Purchase #4 $104.88   3.505%   $108.556   $108.56   $108.55   $108.60  
  Purchase #5 $12.88   11.717%   $14.3891   $14.39   $14.40   $14.40  
  Purchase #6 $177.58   3.491%   $183.7793   $183.78   $183.80   $183.80  
  Purchase #7 $196.42   12.402%   $220.78   $220.78   $220.80   $220.80  
  7 purchase totals = $698.48       $750.5949   $750.60   $750.65   $750.70