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 $246.51   12.235%   $276.6705   $276.67   $276.65   $276.70  
  Purchase #2 $85.81   9.474%   $93.9396   $93.94   $93.95   $93.90  
  Purchase #3 $52.92   9.739%   $58.0739   $58.07   $58.05   $58.10  
  Purchase #4 $23.91   10.402%   $26.3971   $26.40   $26.40   $26.40  
  Purchase #5 $187.36   12.653%   $211.0667   $211.07   $211.05   $211.10  
  Purchase #6 $56.68   12.384%   $63.6993   $63.70   $63.70   $63.70  
  Purchase #7 $201.41   5.535%   $212.558   $212.56   $212.55   $212.60  
  7 purchase totals = $854.60       $942.4051   $942.41   $942.35   $942.50