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 $106.86   11.793%   $119.462   $119.46   $119.45   $119.50  
  Purchase #2 $106.79   12.238%   $119.859   $119.86   $119.85   $119.90  
  Purchase #3 $216.52   4.650%   $226.5882   $226.59   $226.60   $226.60  
  Purchase #4 $44.62   3.774%   $46.304   $46.30   $46.30   $46.30  
  Purchase #5 $195.86   8.371%   $212.2554   $212.26   $212.25   $212.30  
  Purchase #6 $54.79   3.157%   $56.5197   $56.52   $56.50   $56.50  
  Purchase #7 $225.26   6.626%   $240.1857   $240.19   $240.20   $240.20  
  7 purchase totals = $950.70       $1,021.1740   $1,021.18   $1,021.15   $1,021.30