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 $168.83   9.314%   $184.5548   $184.55   $184.55   $184.60  
  Purchase #2 $147.89   11.261%   $164.5439   $164.54   $164.55   $164.50  
  Purchase #3 $202.29   12.207%   $226.9835   $226.98   $227.00   $227.00  
  Purchase #4 $230.57   12.713%   $259.8824   $259.88   $259.90   $259.90  
  Purchase #5 $32.73   13.249%   $37.0664   $37.07   $37.05   $37.10  
  Purchase #6 $97.95   12.323%   $110.0204   $110.02   $110.00   $110.00  
  Purchase #7 $74.36   7.784%   $80.1482   $80.15   $80.15   $80.10  
  7 purchase totals = $954.62       $1,063.1996   $1,063.19   $1,063.20   $1,063.20