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 $246.72   8.402%   $267.4494   $267.45   $267.45   $267.40  
  Purchase #2 $20.91   9.535%   $22.9038   $22.90   $22.90   $22.90  
  Purchase #3 $87.84   8.831%   $95.5972   $95.60   $95.60   $95.60  
  Purchase #4 $203.60   9.330%   $222.5959   $222.60   $222.60   $222.60  
  Purchase #5 $95.73   12.743%   $107.9289   $107.93   $107.95   $107.90  
  Purchase #6 $25.39   4.302%   $26.4823   $26.48   $26.50   $26.50  
  Purchase #7 $247.25   11.292%   $275.1695   $275.17   $275.15   $275.20  
  7 purchase totals = $927.44       $1,018.1270   $1,018.13   $1,018.15   $1,018.10