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 $54.70   8.463%   $59.3293   $59.33   $59.35   $59.30  
  Purchase #2 $85.29   6.770%   $91.0641   $91.06   $91.05   $91.10  
  Purchase #3 $246.30   3.111%   $253.9624   $253.96   $253.95   $254.00  
  Purchase #4 $97.44   6.585%   $103.8564   $103.86   $103.85   $103.90  
  Purchase #5 $45.53   3.207%   $46.9901   $46.99   $47.00   $47.00  
  Purchase #6 $123.63   5.390%   $130.2937   $130.29   $130.30   $130.30  
  Purchase #7 $88.51   11.285%   $98.4984   $98.50   $98.50   $98.50  
  7 purchase totals = $741.40       $783.9944   $783.99   $784.00   $784.10