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 $235.53   8.760%   $256.1624   $256.16   $256.15   $256.20  
  Purchase #2 $184.94   7.270%   $198.3851   $198.39   $198.40   $198.40  
  Purchase #3 $174.56   8.408%   $189.237   $189.24   $189.25   $189.20  
  Purchase #4 $91.43   6.585%   $97.4507   $97.45   $97.45   $97.50  
  Purchase #5 $208.49   8.771%   $226.7767   $226.78   $226.80   $226.80  
  Purchase #6 $193.84   6.253%   $205.9608   $205.96   $205.95   $206.00  
  Purchase #7 $174.29   5.221%   $183.3897   $183.39   $183.40   $183.40  
  7 purchase totals = $1,263.08       $1,357.3624   $1,357.37   $1,357.40   $1,357.50