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 $145.46   13.620%   $165.2717   $165.27   $165.25   $165.30  
  Purchase #2 $165.39   9.226%   $180.6489   $180.65   $180.65   $180.60  
  Purchase #3 $161.30   9.818%   $177.1364   $177.14   $177.15   $177.10  
  Purchase #4 $88.40   7.350%   $94.8974   $94.90   $94.90   $94.90  
  Purchase #5 $250.56   12.175%   $281.0657   $281.07   $281.05   $281.10  
  Purchase #6 $195.79   9.341%   $214.0787   $214.08   $214.10   $214.10  
  Purchase #7 $107.51   12.305%   $120.7391   $120.74   $120.75   $120.70  
  7 purchase totals = $1,114.41       $1,233.8379   $1,233.85   $1,233.85   $1,233.80