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 $228.47   11.230%   $254.1272   $254.13   $254.15   $254.10  
  Purchase #2 $63.57   5.868%   $67.3003   $67.30   $67.30   $67.30  
  Purchase #3 $12.98   9.748%   $14.2453   $14.25   $14.25   $14.20  
  Purchase #4 $237.85   12.337%   $267.1936   $267.19   $267.20   $267.20  
  Purchase #5 $236.59   3.390%   $244.6104   $244.61   $244.60   $244.60  
  Purchase #6 $150.99   6.638%   $161.0127   $161.01   $161.00   $161.00  
  Purchase #7 $16.53   11.615%   $18.45   $18.45   $18.45   $18.50  
  7 purchase totals = $946.98       $1,026.9395   $1,026.94   $1,026.95   $1,026.90