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 $94.82   12.749%   $106.9086   $106.91   $106.90   $106.90  
  Purchase #2 $213.34   3.468%   $220.7386   $220.74   $220.75   $220.70  
  Purchase #3 $248.28   9.457%   $271.7598   $271.76   $271.75   $271.80  
  Purchase #4 $24.72   5.718%   $26.1335   $26.13   $26.15   $26.10  
  Purchase #5 $75.92   11.386%   $84.5643   $84.56   $84.55   $84.60  
  Purchase #6 $172.31   8.292%   $186.5979   $186.60   $186.60   $186.60  
  Purchase #7 $124.80   7.275%   $133.8792   $133.88   $133.90   $133.90  
  7 purchase totals = $954.19       $1,030.5819   $1,030.58   $1,030.60   $1,030.60