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 $49.35   6.867%   $52.7389   $52.74   $52.75   $52.70  
  Purchase #2 $160.80   4.259%   $167.6485   $167.65   $167.65   $167.60  
  Purchase #3 $244.85   8.298%   $265.1677   $265.17   $265.15   $265.20  
  Purchase #4 $164.34   7.829%   $177.2062   $177.21   $177.20   $177.20  
  Purchase #5 $6.57   11.426%   $7.3207   $7.32   $7.30   $7.30  
  Purchase #6 $186.54   7.442%   $200.4223   $200.42   $200.40   $200.40  
  Purchase #7 $183.66   4.766%   $192.4132   $192.41   $192.40   $192.40  
  7 purchase totals = $996.11       $1,062.9175   $1,062.92   $1,062.85   $1,062.80