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 $84.87   11.702%   $94.8015   $94.80   $94.80   $94.80  
  Purchase #2 $103.71   4.119%   $107.9818   $107.98   $108.00   $108.00  
  Purchase #3 $156.29   9.147%   $170.5858   $170.59   $170.60   $170.60  
  Purchase #4 $110.48   3.463%   $114.3059   $114.31   $114.30   $114.30  
  Purchase #5 $201.40   11.873%   $225.3122   $225.31   $225.30   $225.30  
  Purchase #6 $238.69   8.813%   $259.7257   $259.73   $259.75   $259.70  
  Purchase #7 $201.34   8.580%   $218.615   $218.62   $218.60   $218.60  
  7 purchase totals = $1,096.78       $1,191.3279   $1,191.34   $1,191.35   $1,191.30