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 $20.62   11.323%   $22.9548   $22.95   $22.95   $23.00  
  Purchase #2 $228.82   8.758%   $248.8601   $248.86   $248.85   $248.90  
  Purchase #3 $12.71   9.696%   $13.9424   $13.94   $13.95   $13.90  
  Purchase #4 $119.34   12.590%   $134.3649   $134.36   $134.35   $134.40  
  Purchase #5 $203.91   4.107%   $212.2846   $212.28   $212.30   $212.30  
  Purchase #6 $52.94   5.160%   $55.6717   $55.67   $55.65   $55.70  
  Purchase #7 $231.57   9.170%   $252.805   $252.81   $252.80   $252.80  
  7 purchase totals = $869.91       $940.8835   $940.87   $940.85   $941.00