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 $211.93   6.642%   $226.0064   $226.01   $226.00   $226.00  
  Purchase #2 $38.65   7.788%   $41.6601   $41.66   $41.65   $41.70  
  Purchase #3 $101.62   13.667%   $115.5084   $115.51   $115.50   $115.50  
  Purchase #4 $160.91   11.193%   $178.9207   $178.92   $178.90   $178.90  
  Purchase #5 $203.55   9.731%   $223.3575   $223.36   $223.35   $223.40  
  Purchase #6 $198.58   11.697%   $221.8079   $221.81   $221.80   $221.80  
  Purchase #7 $216.56   13.479%   $245.7501   $245.75   $245.75   $245.80  
  7 purchase totals = $1,131.80       $1,253.0111   $1,253.02   $1,252.95   $1,253.10