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 $22.44   3.200%   $23.1581   $23.16   $23.15   $23.20  
  Purchase #2 $212.68   9.386%   $232.6421   $232.64   $232.65   $232.60  
  Purchase #3 $144.72   4.346%   $151.0095   $151.01   $151.00   $151.00  
  Purchase #4 $239.68   12.371%   $269.3308   $269.33   $269.35   $269.30  
  Purchase #5 $54.34   10.172%   $59.8675   $59.87   $59.85   $59.90  
  Purchase #6 $207.67   12.301%   $233.2155   $233.22   $233.20   $233.20  
  Purchase #7 $91.61   12.562%   $103.118   $103.12   $103.10   $103.10  
  7 purchase totals = $973.14       $1,072.3415   $1,072.35   $1,072.30   $1,072.30