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 $156.58   3.778%   $162.4956   $162.50   $162.50   $162.50  
  Purchase #2 $56.55   6.140%   $60.0222   $60.02   $60.00   $60.00  
  Purchase #3 $120.79   6.283%   $128.3792   $128.38   $128.40   $128.40  
  Purchase #4 $241.88   6.564%   $257.757   $257.76   $257.75   $257.80  
  Purchase #5 $211.49   11.468%   $235.7437   $235.74   $235.75   $235.70  
  Purchase #6 $65.55   5.431%   $69.11   $69.11   $69.10   $69.10  
  Purchase #7 $211.77   13.705%   $240.7931   $240.79   $240.80   $240.80  
  7 purchase totals = $1,064.61       $1,154.3008   $1,154.30   $1,154.30   $1,154.30