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 $57.46   3.264%   $59.3355   $59.34   $59.35   $59.30  
  Purchase #2 $212.95   8.290%   $230.6036   $230.60   $230.60   $230.60  
  Purchase #3 $90.37   9.837%   $99.2597   $99.26   $99.25   $99.30  
  Purchase #4 $121.81   4.150%   $126.8651   $126.87   $126.85   $126.90  
  Purchase #5 $96.68   8.393%   $104.7944   $104.79   $104.80   $104.80  
  Purchase #6 $105.88   9.584%   $116.0275   $116.03   $116.05   $116.00  
  Purchase #7 $211.48   5.521%   $223.1558   $223.16   $223.15   $223.20  
  7 purchase totals = $896.63       $960.0416   $960.05   $960.05   $960.10