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 $156.69   5.416%   $165.1763   $165.18   $165.20   $165.20  
  Purchase #2 $84.54   11.167%   $93.9806   $93.98   $94.00   $94.00  
  Purchase #3 $152.60   9.457%   $167.0314   $167.03   $167.05   $167.00  
  Purchase #4 $218.93   12.207%   $245.6548   $245.65   $245.65   $245.70  
  Purchase #5 $236.81   5.190%   $249.1004   $249.10   $249.10   $249.10  
  Purchase #6 $146.39   3.729%   $151.8489   $151.85   $151.85   $151.80  
  Purchase #7 $52.36   8.733%   $56.9326   $56.93   $56.95   $56.90  
  7 purchase totals = $1,048.32       $1,129.7250   $1,129.72   $1,129.80   $1,129.70