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 $170.98   13.774%   $194.5308   $194.53   $194.55   $194.50  
  Purchase #2 $62.28   5.737%   $65.853   $65.85   $65.85   $65.90  
  Purchase #3 $53.88   6.281%   $57.2642   $57.26   $57.25   $57.30  
  Purchase #4 $214.83   10.813%   $238.0596   $238.06   $238.05   $238.10  
  Purchase #5 $240.71   13.745%   $273.7956   $273.80   $273.80   $273.80  
  Purchase #6 $21.72   7.237%   $23.2919   $23.29   $23.30   $23.30  
  Purchase #7 $160.49   4.412%   $167.5708   $167.57   $167.55   $167.60  
  7 purchase totals = $924.89       $1,020.3659   $1,020.36   $1,020.35   $1,020.50