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 $204.43   13.610%   $232.2529   $232.25   $232.25   $232.30  
  Purchase #2 $195.74   13.339%   $221.8498   $221.85   $221.85   $221.80  
  Purchase #3 $165.61   6.181%   $175.8464   $175.85   $175.85   $175.80  
  Purchase #4 $225.96   12.574%   $254.3722   $254.37   $254.35   $254.40  
  Purchase #5 $9.82   7.701%   $10.5762   $10.58   $10.60   $10.60  
  Purchase #6 $165.95   12.142%   $186.0996   $186.10   $186.10   $186.10  
  Purchase #7 $71.59   6.199%   $76.0279   $76.03   $76.05   $76.00  
  7 purchase totals = $1,039.10       $1,157.0250   $1,157.03   $1,157.05   $1,157.00