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 $247.58   6.636%   $264.0094   $264.01   $264.00   $264.00  
  Purchase #2 $171.72   12.681%   $193.4958   $193.50   $193.50   $193.50  
  Purchase #3 $31.58   8.467%   $34.2539   $34.25   $34.25   $34.30  
  Purchase #4 $226.46   3.366%   $234.0826   $234.08   $234.10   $234.10  
  Purchase #5 $209.39   13.484%   $237.6241   $237.62   $237.60   $237.60  
  Purchase #6 $212.64   12.447%   $239.1073   $239.11   $239.10   $239.10  
  Purchase #7 $44.74   10.227%   $49.3156   $49.32   $49.30   $49.30  
  7 purchase totals = $1,144.11       $1,251.8887   $1,251.89   $1,251.85   $1,251.90