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 $192.74   12.705%   $217.2276   $217.23   $217.25   $217.20  
  Purchase #2 $95.63   12.837%   $107.906   $107.91   $107.90   $107.90  
  Purchase #3 $81.82   8.561%   $88.8246   $88.82   $88.80   $88.80  
  Purchase #4 $30.98   8.195%   $33.5188   $33.52   $33.50   $33.50  
  Purchase #5 $109.36   11.280%   $121.6958   $121.70   $121.70   $121.70  
  Purchase #6 $180.73   12.867%   $203.9845   $203.98   $204.00   $204.00  
  Purchase #7 $192.33   13.723%   $218.7234   $218.72   $218.70   $218.70  
  7 purchase totals = $883.59       $991.8807   $991.88   $991.85   $991.80