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 $124.64   13.367%   $141.3006   $141.30   $141.30   $141.30  
  Purchase #2 $249.53   6.487%   $265.717   $265.72   $265.70   $265.70  
  Purchase #3 $95.57   7.153%   $102.4061   $102.41   $102.40   $102.40  
  Purchase #4 $181.35   9.559%   $198.6852   $198.69   $198.70   $198.70  
  Purchase #5 $57.85   5.463%   $61.0103   $61.01   $61.00   $61.00  
  Purchase #6 $174.55   11.590%   $194.7803   $194.78   $194.80   $194.80  
  Purchase #7 $208.65   3.827%   $216.635   $216.64   $216.65   $216.60  
  7 purchase totals = $1,092.14       $1,180.5345   $1,180.55   $1,180.55   $1,180.50