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 $231.89   6.269%   $246.4272   $246.43   $246.45   $246.40  
  Purchase #2 $176.57   11.759%   $197.3329   $197.33   $197.35   $197.30  
  Purchase #3 $167.36   4.218%   $174.4192   $174.42   $174.40   $174.40  
  Purchase #4 $232.53   10.109%   $256.0365   $256.04   $256.05   $256.00  
  Purchase #5 $115.40   4.593%   $120.7003   $120.70   $120.70   $120.70  
  Purchase #6 $42.48   11.123%   $47.2051   $47.21   $47.20   $47.20  
  Purchase #7 $49.82   12.357%   $55.9763   $55.98   $56.00   $56.00  
  7 purchase totals = $1,016.05       $1,098.0975   $1,098.11   $1,098.15   $1,098.00