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 $34.87   5.260%   $36.7042   $36.70   $36.70   $36.70  
  Purchase #2 $101.41   5.802%   $107.2938   $107.29   $107.30   $107.30  
  Purchase #3 $224.65   4.614%   $235.0154   $235.02   $235.00   $235.00  
  Purchase #4 $39.85   13.367%   $45.1767   $45.18   $45.20   $45.20  
  Purchase #5 $64.82   12.570%   $72.9679   $72.97   $72.95   $73.00  
  Purchase #6 $163.33   7.302%   $175.2564   $175.26   $175.25   $175.30  
  Purchase #7 $135.66   5.847%   $143.592   $143.59   $143.60   $143.60  
  7 purchase totals = $764.59       $816.0064   $816.01   $816.00   $816.10