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 $144.66   4.764%   $151.5516   $151.55   $151.55   $151.60  
  Purchase #2 $200.70   5.769%   $212.2784   $212.28   $212.30   $212.30  
  Purchase #3 $25.53   9.359%   $27.9194   $27.92   $27.90   $27.90  
  Purchase #4 $84.55   11.381%   $94.1726   $94.17   $94.15   $94.20  
  Purchase #5 $165.68   3.582%   $171.6147   $171.61   $171.60   $171.60  
  Purchase #6 $172.49   13.513%   $195.7986   $195.80   $195.80   $195.80  
  Purchase #7 $201.56   4.240%   $210.1061   $210.11   $210.10   $210.10  
  7 purchase totals = $995.17       $1,063.4414   $1,063.44   $1,063.40   $1,063.50