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 $19.61   4.369%   $20.4668   $20.47   $20.45   $20.50  
  Purchase #2 $121.28   6.539%   $129.2105   $129.21   $129.20   $129.20  
  Purchase #3 $172.54   9.551%   $189.0193   $189.02   $189.00   $189.00  
  Purchase #4 $235.42   8.784%   $256.0993   $256.10   $256.10   $256.10  
  Purchase #5 $200.33   3.623%   $207.588   $207.59   $207.60   $207.60  
  Purchase #6 $169.53   8.303%   $183.6061   $183.61   $183.60   $183.60  
  Purchase #7 $170.85   11.109%   $189.8297   $189.83   $189.85   $189.80  
  7 purchase totals = $1,089.56       $1,175.8197   $1,175.83   $1,175.80   $1,175.80