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 $178.36   4.374%   $186.1615   $186.16   $186.15   $186.20  
  Purchase #2 $223.90   6.455%   $238.3527   $238.35   $238.35   $238.40  
  Purchase #3 $90.33   4.827%   $94.6902   $94.69   $94.70   $94.70  
  Purchase #4 $148.41   5.647%   $156.7907   $156.79   $156.80   $156.80  
  Purchase #5 $177.72   5.852%   $188.1202   $188.12   $188.10   $188.10  
  Purchase #6 $46.98   4.263%   $48.9828   $48.98   $49.00   $49.00  
  Purchase #7 $233.84   5.590%   $246.9117   $246.91   $246.90   $246.90  
  7 purchase totals = $1,099.54       $1,160.0098   $1,160.00   $1,160.00   $1,160.10