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 $202.99   13.291%   $229.9694   $229.97   $229.95   $230.00  
  Purchase #2 $59.28   5.582%   $62.589   $62.59   $62.60   $62.60  
  Purchase #3 $167.83   7.373%   $180.2041   $180.20   $180.20   $180.20  
  Purchase #4 $246.43   12.470%   $277.1598   $277.16   $277.15   $277.20  
  Purchase #5 $215.85   4.594%   $225.7661   $225.77   $225.75   $225.80  
  Purchase #6 $56.33   5.566%   $59.4653   $59.47   $59.45   $59.50  
  Purchase #7 $93.47   3.245%   $96.5031   $96.50   $96.50   $96.50  
  7 purchase totals = $1,042.18       $1,131.6568   $1,131.66   $1,131.60   $1,131.80