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 $250.54   10.465%   $276.759   $276.76   $276.75   $276.80  
  Purchase #2 $118.90   10.265%   $131.1051   $131.11   $131.10   $131.10  
  Purchase #3 $215.95   11.614%   $241.0304   $241.03   $241.05   $241.00  
  Purchase #4 $67.74   13.788%   $77.08   $77.08   $77.10   $77.10  
  Purchase #5 $191.55   12.352%   $215.2103   $215.21   $215.20   $215.20  
  Purchase #6 $49.46   9.616%   $54.2161   $54.22   $54.20   $54.20  
  Purchase #7 $159.61   9.146%   $174.2079   $174.21   $174.20   $174.20  
  7 purchase totals = $1,053.75       $1,169.6088   $1,169.62   $1,169.60   $1,169.60