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 $190.94   11.401%   $212.7091   $212.71   $212.70   $212.70  
  Purchase #2 $23.71   10.318%   $26.1564   $26.16   $26.15   $26.20  
  Purchase #3 $226.73   9.331%   $247.8862   $247.89   $247.90   $247.90  
  Purchase #4 $32.52   3.865%   $33.7769   $33.78   $33.80   $33.80  
  Purchase #5 $241.43   3.318%   $249.4406   $249.44   $249.45   $249.40  
  Purchase #6 $64.89   7.437%   $69.7159   $69.72   $69.70   $69.70  
  Purchase #7 $185.76   6.833%   $198.453   $198.45   $198.45   $198.50  
  7 purchase totals = $965.98       $1,038.1381   $1,038.15   $1,038.15   $1,038.20