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 $126.83   5.282%   $133.5292   $133.53   $133.55   $133.50  
  Purchase #2 $41.67   3.143%   $42.9797   $42.98   $43.00   $43.00  
  Purchase #3 $218.49   10.656%   $241.7723   $241.77   $241.75   $241.80  
  Purchase #4 $111.98   7.212%   $120.056   $120.06   $120.05   $120.10  
  Purchase #5 $22.41   5.182%   $23.5713   $23.57   $23.55   $23.60  
  Purchase #6 $239.50   7.435%   $257.3068   $257.31   $257.30   $257.30  
  Purchase #7 $183.44   9.819%   $201.452   $201.45   $201.45   $201.50  
  7 purchase totals = $944.32       $1,020.6673   $1,020.67   $1,020.65   $1,020.80