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 $75.51   5.641%   $79.7695   $79.77   $79.75   $79.80  
  Purchase #2 $91.80   7.364%   $98.5602   $98.56   $98.55   $98.60  
  Purchase #3 $88.31   4.543%   $92.3219   $92.32   $92.30   $92.30  
  Purchase #4 $125.54   4.342%   $130.9909   $130.99   $131.00   $131.00  
  Purchase #5 $169.90   6.506%   $180.9537   $180.95   $180.95   $181.00  
  Purchase #6 $208.77   11.453%   $232.6804   $232.68   $232.70   $232.70  
  Purchase #7 $229.59   7.801%   $247.5003   $247.50   $247.50   $247.50  
  7 purchase totals = $989.42       $1,062.7769   $1,062.77   $1,062.75   $1,062.90