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 $86.50   12.396%   $97.2225   $97.22   $97.20   $97.20  
  Purchase #2 $238.97   3.568%   $247.4964   $247.50   $247.50   $247.50  
  Purchase #3 $199.70   6.332%   $212.345   $212.35   $212.35   $212.30  
  Purchase #4 $84.62   8.842%   $92.1021   $92.10   $92.10   $92.10  
  Purchase #5 $235.73   7.204%   $252.712   $252.71   $252.70   $252.70  
  Purchase #6 $218.50   3.535%   $226.224   $226.22   $226.20   $226.20  
  Purchase #7 $83.58   5.191%   $87.9186   $87.92   $87.90   $87.90  
  7 purchase totals = $1,147.60       $1,216.0206   $1,216.02   $1,215.95   $1,215.90