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 $192.26   10.212%   $211.8936   $211.89   $211.90   $211.90  
  Purchase #2 $236.99   3.639%   $245.6141   $245.61   $245.60   $245.60  
  Purchase #3 $67.90   10.157%   $74.7966   $74.80   $74.80   $74.80  
  Purchase #4 $121.49   11.817%   $135.8465   $135.85   $135.85   $135.80  
  Purchase #5 $225.28   4.459%   $235.3252   $235.33   $235.35   $235.30  
  Purchase #6 $44.55   5.352%   $46.9343   $46.93   $46.95   $46.90  
  Purchase #7 $72.87   11.473%   $81.2304   $81.23   $81.25   $81.20  
  7 purchase totals = $961.34       $1,031.6407   $1,031.64   $1,031.70   $1,031.50