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 $54.85   8.688%   $59.6154   $59.62   $59.60   $59.60  
  Purchase #2 $193.55   7.424%   $207.9192   $207.92   $207.90   $207.90  
  Purchase #3 $157.98   6.171%   $167.7289   $167.73   $167.75   $167.70  
  Purchase #4 $209.32   8.345%   $226.7878   $226.79   $226.80   $226.80  
  Purchase #5 $218.41   12.498%   $245.7069   $245.71   $245.70   $245.70  
  Purchase #6 $97.57   7.743%   $105.1248   $105.12   $105.10   $105.10  
  Purchase #7 $60.92   8.799%   $66.2804   $66.28   $66.30   $66.30  
  7 purchase totals = $992.60       $1,079.1634   $1,079.17   $1,079.15   $1,079.10