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 $203.38   11.702%   $227.1795   $227.18   $227.20   $227.20  
  Purchase #2 $34.59   13.349%   $39.2074   $39.21   $39.20   $39.20  
  Purchase #3 $107.37   5.755%   $113.5491   $113.55   $113.55   $113.50  
  Purchase #4 $249.39   8.225%   $269.9023   $269.90   $269.90   $269.90  
  Purchase #5 $55.82   9.262%   $60.99   $60.99   $61.00   $61.00  
  Purchase #6 $240.47   6.737%   $256.6705   $256.67   $256.65   $256.70  
  Purchase #7 $91.47   4.868%   $95.9228   $95.92   $95.90   $95.90  
  7 purchase totals = $982.49       $1,063.4216   $1,063.42   $1,063.40   $1,063.40