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 $188.39   8.254%   $203.9397   $203.94   $203.95   $203.90  
  Purchase #2 $20.47   13.346%   $23.2019   $23.20   $23.20   $23.20  
  Purchase #3 $58.67   3.608%   $60.7868   $60.79   $60.80   $60.80  
  Purchase #4 $169.73   13.411%   $192.4925   $192.49   $192.50   $192.50  
  Purchase #5 $88.96   8.611%   $96.6203   $96.62   $96.60   $96.60  
  Purchase #6 $197.59   12.469%   $222.2275   $222.23   $222.25   $222.20  
  Purchase #7 $202.28   3.514%   $209.3881   $209.39   $209.40   $209.40  
  7 purchase totals = $926.09       $1,008.6568   $1,008.66   $1,008.70   $1,008.60